Quote Originally Posted by Risvertasashi View Post
It starts as soon as you place the star. It will also detonate at the end of the second cycle automatically, so you can time it such that you don't need to manually detonate. (Mildly interesting but useless sidenote: The detonation command has a CD of 5s)

If you let it expire natually, ES will resume its place on your hotbar with 39s left on the countdown (assuming good latency).
Also useless sidenote. CO will extend the duration of ES, making it take even long to power up(or letting it last a longer time when it is powered up).