From my observations on the PTR with Windward Heart (normal) has been:
DOES proc off of hot crits.
The spell proc is called "Nick of Time" (no PTR datamine link at the moment)
The ICD feels to be BELOW 45 seconds with some approximation by others (
link). My testing in a 25 LFR raid suggests that a 25 second - 35 second ICD correlates to the proc rate compared to the fight duration (
WoL Link) [Sephinia is the druid with the trinket]
Note: The windward heart trinket is seeing 6% - 9% of healing done over the course of a boss encounter.