So, nawr and rwan both mean now? Does any combination of n, a, r, and w mean now?
No, just nawr and rŵan.
They're both derived from the same source, more or less:
yn awr hon ("at this time"?) - yrŵan - ’rŵan
yn awr ("at a time"?) - ’nawr
GPC spells them with an apostrophe (see the entries for yrŵan, ’rŵan and nawr), the Duolingo course without.
Too bad, I was hoping that, in Welsh, a word could always mean the same thing whether spelled forward or backward.
Isn't awr hour not time? I've always been taught that amser is the word for time.