Learn Hardcore German: Ich lasse mich nur überreden, wenn ich genug Zeit habe, mich darauf vorzubereiten. - I only let myself be persuaded when I have enough time to prepare for it.

Lassen plus a reflexive pronoun (ich lasse mich …) often means “I allow/let this happen to me,” so ich lasse mich überreden literally is “I let myself be persuaded.”
Werden + past participle (ich werde überredet) is the normal passive “I am being persuaded,” which doesn’t say anything about whether I agree to it.

So:

Ich lasse mich überreden = I am willing to be persuaded / I allow others to persuade me.
Ich werde überredet = I am (being) persuaded (just a passive description, less about my will).

In this sentence, the point is about willingness/permission, so lassen is better than werden.

What exactly does lassen mean in this sentence?

Here lassen is used in its “causative/permessive” meaning: to let, to allow, to permit (something to be done).

With a reflexive pronoun:

jemanden überreden = to persuade someone
sich überreden lassen = to let oneself be persuaded / allow others to persuade one

So ich lasse mich überreden focuses on my decision to allow persuasion, not on someone else’s action in a neutral passive way.

Why do we have mich twice: ich lasse mich …, wenn ich … mich darauf vorzubereiten? Is that necessary?

Yes, both mich are grammatically required, but they belong to different verbs:

ich lasse mich überreden – mich is the object of lasse (reflexive with lassen).
ich habe … mich darauf vorzubereiten – mich is the reflexive object of vorbereiten.

Each reflexive verb needs its own reflexive pronoun in its own clause or infinitive construction.
You cannot “reuse” the first mich for vorbereiten, so dropping the second mich (… Zeit habe, darauf vorzubereiten) would be wrong.

What is the function of nur in Ich lasse mich nur überreden and could it be placed somewhere else?

Nur here means “only,” limiting the statement: “I only let myself be persuaded (under certain conditions).”

Ich lasse mich nur überreden, wenn … = I only allow myself to be persuaded if …

If you move nur, you change the focus:

Nur ich lasse mich überreden, wenn … = Only I let myself be persuaded (others don’t).
Ich lasse mich überreden, nur wenn ich genug Zeit habe … = I let myself be persuaded, but only when I have enough time…

So the position of nur affects what exactly is being limited (I / the action / the condition). In the original, it restricts the whole act of being persuaded.

Why does the verb go to the end in wenn ich genug Zeit habe, mich darauf vorzubereiten?

Wenn introduces a subordinate clause. In German subordinate clauses, the finite verb goes to the very end:

ich habe genug Zeit (main clause: verb in position 2)
wenn ich genug Zeit habe (subordinate clause: verb habe at the end)

The same applies inside the infinitive phrase:

ich bereite mich darauf vor (main clause, separable verb vorbereiten)
mich darauf vorzubereiten (infinitive clause: vorzubereiten at the end, with zu in the middle of the verb).

What is the difference between wenn here and falls or als?

In this sentence, wenn means “if/whenever” in a general, repeatable sense:

wenn ich genug Zeit habe = if I (ever) have enough time / whenever I have enough time.

Comparisons:

falls ich genug Zeit habe is close to “in case I have enough time.” It sounds a bit more hypothetical, slightly more formal.
als ich genug Zeit hatte refers to a single past event (“when I once had enough time”), so it doesn’t fit the general condition expressed here.

So wenn is the standard choice for general conditions in present or future time.

What does darauf mean in mich darauf vorzubereiten?

Darauf is a da- + preposition compound: da + auf = “on it / for it.”
It stands in for an object with auf:

sich auf etwas vorbereiten = to prepare (oneself) for something
sich darauf vorbereiten = to prepare (oneself) for it (that previously mentioned thing)

Here darauf refers back to the situation or action you will be persuaded into. So mich darauf vorzubereiten = “to prepare myself for that (thing).”

Why is the phrase mich darauf vorzubereiten at the very end of the sentence?

Mich darauf vorzubereiten is an infinitive clause with zu. In German, such infinitive clauses normally go to the end of their clause:

ich habe Zeit, mich darauf vorzubereiten
wenn ich Zeit habe, mich darauf vorzubereiten

Inside the infinitive clause:

vorbereiten (the infinitive) goes at the end,
zu is attached to it (vorzubereiten),
objects and pronouns (mich, darauf) stand before the infinitive.

So the order mich darauf vorzubereiten is the standard pattern: pronoun → da-word → zu + infinitive at the end.

Which case is mich here: accusative or dative? And why?

In both places mich is accusative:

ich lasse mich überreden
- The verb is effectively jemanden überreden (to persuade someone → someone in accusative).
- In the reflexive structure sich überreden lassen, the reflexive pronoun is also accusative: mich.
mich darauf vorzubereiten
- sich auf etwas vorbereiten also takes the reflexive in the accusative case: ich bereite mich vor.

There is no dative reflexive here because the verbs involved naturally take an accusative object.

What is the nuance of überreden compared to überzeugen?

Both can translate as “to persuade/convince,” but they differ slightly:

überzeugen: to convince by good arguments, evidence, reasoning.
→ more neutral or positive.
überreden: to talk someone into something, sometimes against their initial will or better judgment.
→ can sound more pushy or manipulative.

So ich lasse mich überreden suggests “I let myself be talked into it,” not just “I become rationally convinced.”

Why are there commas in … überreden, wenn ich genug Zeit habe, mich darauf vorzubereiten?

Two different comma rules are at work:

überreden, wenn ich genug Zeit habe …
- A comma is mandatory before a subordinate clause introduced by wenn.
… wenn ich genug Zeit habe, mich darauf vorzubereiten.
- mich darauf vorzubereiten is an infinitive clause with zu that is expanded and clearly connected to the noun Zeit (“time to prepare myself for it”).
- In such cases, a comma is standard (and in most modern style guides, recommended / often obligatory): Zeit, mich darauf vorzubereiten.

So both commas follow normal German punctuation rules for subclauses and infinitive clauses.

Could you rephrase the sentence in a more “literal” or more formal way in German?

A bit more explicit / formal would be:

Ich bin nur bereit, mich überreden zu lassen, wenn ich genug Zeit habe, mich darauf vorzubereiten.

This keeps the same meaning but makes bereit (“willing”) explicit and uses überreden zu lassen, which some learners find more transparent than ich lasse mich überreden.

Another possible variant with a fronted condition:

Nur wenn ich genug Zeit habe, mich darauf vorzubereiten, lasse ich mich überreden.

Why is German present tense used here, even though in English we might say “I will only let myself be persuaded …”?

German often uses the present tense for general statements about the future, especially when expressing conditions or rules:

Ich lasse mich nur überreden, wenn ich genug Zeit habe …
literally: “I let myself be persuaded, if I have enough time …”

In English we often switch to the future in such contexts:

“I will only let myself be persuaded if I have enough time …”

But in German, future tense (ich werde …) is not required here; the present tense already naturally covers a general future condition.