Actually, according to people in the know, you should hold the first use for the first meta to drop, so at 30sec mark, and second you want to delay until cb/nem comes up again. Third use it on cd and fourth comes after second meta and the cycle begins over again.
But then again, BTI is a really strong trinket so doubt any HC trinket in there will be better than it.
https://docs.google.com/spreadsheets..._047I/pubhtml#
In the notes below the list you see the requirement
actions.cooldown+=/use_item,slot=trinket1,if=cooldown.nemesis.remains>30&!buff.metamorphosis.up&cooldown.blad e_dance.remains>3