Earthly star is all about timing, the moment where the skill pop right after the boss use aoe is the best feeling ever (with the minimum of 3 person inside the circle that is)

No need to force it up until 2nd part of the skill, think of it if you manage to pop it at 2nd part = great, 1st part = good.

also question, do we get the skill heal and damage if i let the timer run out? I notice when the 2nd 10s skill is up it get automatically explode, do we get the heal at that time?