2.5 week into flower - thinking of transplanting fr 5G to 10G pot. Have plenty of space

I try to get all my transplanting done preflower. Personally I would avoid transplant at this point unless it's really root bound. That said if you're super careful and think you can pull it off with minimal stress, give it a try. Could go either way but those are the chances we take in this game. Grow to learn as you learn to grow!