I'm curious about "then" at the end of the sentence... for example "Will you be home then?" or "Can you talk then?" Alternatively, "at that time" instead of "then" might work? Would it be "nan lè sa?" or "nan tan sa" maybe?

Haitians primarily use lè sa a or lò sa a  (which means at that time, by then), and yes they sometimes say nan lè sa.
Kèk egzanp:
Will you be there then?
Eske w'ap la lè sa a?

Can you talk then?
Eske w'ap ka pale lò sa a?

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words