for me, it's always when the pond/lake is locked up shore to shore. Where i fish in in what's called the chain of lakes in northern illinois, so in some cases those are very large lakes, or channels that are off of the fox river. In those cases, the whole lake doesn't need to be locked up, just the particular channel you are fishing in. i have been within, say, 20 yards of open water before, and so long as the ice beneath you is 3-4" thick, you are okay. just dont get to close to that edge....
but, i live pretty far south for ice, and have to make a 6 hour trip for hard water, so when i go is usually dead of the winter, and never really have to worry about "transitional" periods.
I hope i at least marginally addressed what you are asking.
