Learn Hardcore Korean: yaksok siganeun geudaero duja. - Let’s keep the appointment time as is.

-자 is the informal propositive ending meaning Let’s (do X).
It implies an inclusive we. You don’t use it to address superiors or in formal situations.
Natural with friends/peers: 약속 시간은 그대로 두자.

How can I say this more politely or formally?

Common options:

Why is -은 (topic) used on 약속 시간 instead of -을/를 (object)?

약속 시간은 marks the appointment time as the topic: As for the appointment time, let’s leave it as is.
You can also use object marking: 약속 시간을 그대로 두자. That’s a straightforward Let’s leave the appointment time as is, with no topical/contrastive nuance.
With -은, there’s often a slight contrast or focus on that item among other possibilities.

Is the subject we? Do I need to say 우리?

-자 already implies we. 우리 is optional and used for emphasis or clarity: 우리 약속 시간은 그대로 두자.
In most contexts, 우리 is omitted.

What does 그대로 두다 literally mean? Any close alternatives?

그대로 두다 = leave/keep something as it is (unchanged).
Very common set phrase; natural in many contexts.
Close alternatives:
- 그대로 놔두다: a bit more colloquial, same meaning.
- 그냥 두다: just leave it (not necessarily stressing unchanged state).
- 유지하다: maintain (more formal/technical).
- 내버려 두다: leave it alone/let it be (can feel hands-off or slightly negative).

Can I use 그냥 instead of 그대로 here?

그대로 emphasizes keeping the current state unchanged.
그냥 means just/simply; it doesn’t specifically stress unchanged state.
Both can work, but 그대로 is crisper for not changing something.
Example nuance:
- 그대로 두자 = let’s keep it as is.
- 그냥 두자 = let’s just leave it (as opposed to taking any action).

Can I drop 시간 and say 약속은 그대로 두자?

Yes, but the nuance shifts:
- 약속 시간은 그대로 두자 targets the time specifically.
- 약속은 그대로 두자 suggests keeping the plan/arrangement itself unchanged (not canceling or altering details). Use the one that matches your intent.

How do I say “Let’s not leave it as is”?

If I want to instruct someone (not suggest) to leave it as is, what should I say?

How do I turn it into a question like “Shall we leave the appointment time as is?”

Is 약속 시간은 그대로 두자 the only natural word order?

It’s the most natural. You can also use the object-marked version: 약속 시간을 그대로 두자.
Avoid scrambling it too much; topics normally come early. Forms like 그대로 약속 시간은 두자 sound odd.

Any quick morphology/meaning breakdown?

약속 (appointment/promise) + 시간 (time) + 은 (topic) + 그대로 (as it is) + 두- (leave/keep) + -자 (let’s).
Overall: As for the appointment time, let’s leave it as it is.

Pronunciation and spacing tips?