Learn Hardcore Danish: Hun afleverer den til min mor, når hun kommer hjem. - She returns it to my mother when she comes home.

Danish commonly uses the present tense to talk about future events, especially in time clauses with når. So Hun afleverer den …, når hun kommer hjem corresponds to English She will deliver it … when she gets home.

You can say Hun vil aflevere den to add intention/willingness, but after når you still say når hun kommer hjem, not når hun vil komme hjem.
Other future-like options: Hun skal aflevere den (is supposed/obliged to), Hun kommer til at aflevere den (is going to/end up delivering it).

Who does the second hun refer to—she or my mother?

As written, it is ambiguous in English, but in Danish the default reading is that the second hun refers back to the main clause subject (the same woman who delivers it). If you mean the mother, Danes usually make it explicit:

Same woman: Hun afleverer den til min mor, når hun kommer hjem.
The mother: Hun afleverer den til min mor, når min mor kommer hjem. (or … når hun er hjemme if the context already makes it clear you mean the mother)
To emphasize the first reading: … når hun selv kommer hjem.

Why is it den and not det?

Den is the object pronoun for common gender (en-words); det is for neuter gender (et-words).

If the thing is an en-word (e.g., bog → bogen), use den: Hun afleverer den …
If it’s an et-word (e.g., brev → brevet), use det: Hun afleverer det … If the antecedent isn’t clear, Danes still pick den/det based on the real noun’s gender, not on a generic English-like it.

What’s the nuance of afleverer compared with giver or leverer?

aflevere: hand in/return/drop off to the rightful place or person (homework, a found item, borrowed things). Very natural with a recipient via til.
give: give as a gift or transfer possession. You can say Hun giver den til min mor; more personal than afleverer.
levere: deliver (often commercially/logistically). Hun leverer den til min mor is okay, but can sound more transactional.

Why is it til min mor? Can I omit til?

With aflevere, the recipient is normally introduced by til: aflevere noget til nogen. You can’t say aflevere nogen noget. With give, both patterns exist: give nogen noget and give noget til nogen are both fine.

Could I use hvis instead of når?

No, not for a time meaning. når = when (every time/whenever/in the future). hvis = if (a condition).

Time: … når hun kommer hjem = when she gets home.
Condition: … hvis hun kommer hjem = if she comes home (it’s uncertain whether she will).

Could I use da instead of når?

Only for a single event in the past. da = when (past, one-time). når = when (habitual or future).

Past: Hun afleverede den til min mor, da hun kom hjem.
Present/future/habitual: Hun afleverer den til min mor, når hun kommer hjem.

What’s the word order rule in the når-clause?

Subordinate clauses in Danish are not V2. The order is typically conjunction + subject + (sentence adverbs like ikke) + finite verb + …

når hun kommer hjem
If you add negation: når hun ikke kommer hjem (note ikke before the finite verb in the subclause)

Where would I put negation or adverbs in the main clause?

Main clauses are V2. The finite verb is second, and sentence adverbs (like ikke, ofte, måske) come after the finite verb.

Negation: Hun afleverer den ikke til min mor, når hun kommer hjem.
Adverb: Hun afleverer den måske til min mor i morgen.

Can I start with the time clause?

Yes. If you front the når-clause, the following main clause still obeys V2, so the finite verb comes before the subject:

Når hun kommer hjem, afleverer hun den til min mor.

Do I need the comma before the når-clause?

Both comma styles are accepted in modern Danish. With the traditional start comma, you put a comma before subordinate clauses: …, når hun kommer hjem. With the newer style, you may omit it: … når hun kommer hjem. If the når-clause comes first, you do put a comma after it either way:

Når hun kommer hjem, afleverer hun den …

Why hjem and not hjemme?

hjem = motion towards home (direction): kommer hjem, går hjem, kører hjem.
hjemme = location at home (state): er hjemme. So når hun kommer hjem = when she gets (arrives) home. If you mean when she is at home, say når hun er hjemme.

Why not til hjem (to home)?

hjem is a special directional adverb; you don’t use til with komme + hjem. However, you can use hjem til when naming a person’s place:

Hun går hjem til min mor (she’s going to my mother’s home).

Should it be hun or hende?

Use hun as a subject and hende as an object.

Subject: Hun afleverer den …
Object/recipient: … til hende.

Why min mor and not mit mor or mine mor?

Possessives agree with the noun’s gender/number:

min
- en-words (singular): min mor
mit
- et-words (singular): mit hus
mine
- all plurals: mine mødre

Can I use hos instead of til?

Different meaning:

til marks the recipient: afleverer den til min mor (to my mother).
hos marks being at someone’s place: afleverer den hos frisøren (at the hairdresser’s). With a person like min mor, hos would mean at her place, not necessarily to her as recipient.

Any quick pronunciation tips for tricky words here?

hjem: initial h is silent; hj sounds like English y, roughly yem.
når: long open vowel; the r is weak.
afleverer: final -er is lightly pronounced; many speakers reduce it.
til often sounds like something close to “tel” in casual speech.
mor has a noticeable glottal catch (stød) for many speakers.