Without tier19 4-set bonus, use rime procs when you are above 40-45 rp (at least from my experience), or you will risk dropping breath, since HB does not provide with RP anymore
droidzone has it, basically you have to make a judgement call, will your breath be in danger of dropping from using the rime proc? If yes don't rime, if no then use it.
The T-19 bonus gives you a much better margin of error to use the rime proc since it does provide some more RP for the Breath to continue.