"Now is a good time."
Translation:Teraz jest dobry czas.
[Noun phrase] to [noun phrase]. Apart from that, yeah (at least so it seems to my sleepy mind right now).
No. In an "X is Y" sentence, Y can only take Instrumental if both X and Y are noun phrases (or if X is a personal pronoun and Y is a noun phrase).
"Teraz jest dobrym czasem" is as if you defined the word "now" by saying that it means "a good time".