The rule is either you self release (HI3 & HI6), *OR* you wait 15 minutes - whichever comes first releases you.
So, it matters if they know you checked your schedule and mail to self release (whether it be via screenshot submitted in a grievance or the company "seeing" that you checked it). I have no clue which apps the company can and cannot see - but as mentioned before, screenshot it so that you are the one holding the evidence that you were properly released if you ignore a phone call before 15 mins have passed.
To me, it's easier to do on MobileFOS because it's one screenshot to show that both have been checked.