"Not now."

Translation: Jangan sekarang.

[Fiza_]

Can I use bukan sekarang or tidak sekarang? Which one is better?

[Rick392366]

Can I use bukan sekarang or tidak sekarang?

Not in a sentence/clause like this, it sounds like an imperative sentence/clause.
'bukan' & 'tidak' are not used in imperative sentences.
'jangan' is used in imperative sentences (as a negation).

[giogiovb]

Thanks for the explanation. I finally understand now why "jangan" is used here! :) Although, if it is an imperative statement/clause, shouldn't it come with an exclamation point at the end?

[Haakon388572]

Imperative statements are written with an exclamation mark only if they are an exclamation, so it is not obligatory.