The trinket cycles between 1 pulse (no buff), 2 pulses, 3 pulses and 4 pulses, then goes back to 1 again, on each use every 1.5 mins. The weakaura shows the cooldown of the trinket, and how many pulses the next use will do.
Use timeline:
0:00 - Single pulse
01:30 - Two pulses
03:00 - Three pulses
04:30 - Four pulses
The 4 pulse use on a large pack can do like 20k dps+ for its duration. I don't have any maths behind this, but I feel like its best to basically send this trinket on cooldown and then hold the 4 pulse for a large pack. You can probably also hold a 3 pulse, but I wouldn't hold 1 or 2 for too long.
If you use another addon to show the CD of stuff on your weakauras, go into the group > Resonant Reservoir Stack Tracker (the one with the actual trinket icon) and uncheck 'Show Text' in text 2 (the one next to %p).