Best time to sync ports?

[Gary Aitken]

Can someone tell me what the best time to synchronize ports is, 
in terms of having a consistent ports tree?

I thought I saw something about the end of the weekend was the best 
time, but I can't find it now.  In any case, is there a period during
which the ports tree is held frozen to get a consistent build?

I try not to rebuild any ports once I get an environment that works 
across all apps I am using.  I'm reluctant to rebuild anything unless 
necessary to correct a problem / bug.

When I encounter a problem with a port I want to sync the ports tree and
rebuild before reporting a bug, but when I do that I want the ports tree
to be consistent enough to build (hopefully) everything in case that's
necessary.

Thanks,

Gary