There is a small hole toward outer edge of stat, if straight up as it should be the system bleeds almost instantly. 5 minutes more than enough.
No way do air pockets make for underheating, rather they do the opposite as do any pressure leaks as a result of the broken plastic hose. That bleeds quick too.
OEM stat opening and closing mean nothing, you must check for absolute 100% closed when cold if chasing your too cold problem.