First right click on the watch: your position and health are saved. Second click within 8 seconds: you return to them.
It is not an escape, it is a bet. Marking at 10 hearts then diving in is giving yourself a free all-in. Marking too late, at 2 hearts, saves nothing at all.
The cooldown starts at the mark, not at the return. That is what keeps the kit honest: if it started at the return, marking would be free, you would keep a mark up permanently, and the kit would become a safety net rather than a decision. Here, a wasted mark costs 60 seconds.
Healing can never be a loss: health is only given back if it is lower than the health saved.
The mark is visible to everyone — particles on the ground. Your opponent knows a return is armed and where it leads: he has to kill you within the eight seconds, or hold the position. An invisible mark would make this kit pure frustration.