yer im waiting one more month so i can start splits, but hey, good way to know... when the lid is really full of bees and they are building burcomb on the tops of your frames (best indication is when 5 out of 10 frames have surplus burcomb ontop) , also you will need brood in all stages and frames completly full of bees aswell... if the honey flow is heavy let them raise their own queen especailly if your queen is holding up the colony well, best indication is too look for good laying pattern, if she is rubbish, then buy a mated queen:P sadly i lost my strong queen and majority of the colony to shb and ants yesterday, so im really lookn forward to gettn another nuc up and running, (must have good honey flow)! and try hard not to feed pollen patties for nucs are really vulnerable to shb and shb are really attracted to pollen even more then the bees believe it or not :P gud luck :P