Just take your feet out well before you think you need to. I'd do both for a little while. Clip one back in while you're waiting at the light.
Another thing to keep in mind is that your clipless system will probably be tighter when new and harder to clip out of, so give yourself some extra room. Do it earlier so you don't panic.
The ONLY time I've ever fallen with my feet clipped in was when i stopped and thought I could hang on to something and intentionally didn't unclip. The other time was with toe straps that were done up too tight, and that was a doozy - middle of a big 4 lane intersection in the left turn lane... tipping..... tipping.... splat.... laughter.