Portrait Holes

[Mindy, a.k.a. CLH]

No: HPFGUIDX 24507

Several times in GoF, someone had to wait outside the common room door to
open the portrait hole for Harry to leave. I am puzzled by this. Does
this mean that the pupils are essentially locked into the Gryffindor
tower until someone opens it from the outside? Is there no other way of
leaving the common room other than waiting for someone to PLEASE chance
by this way? It doesn't seem to make sense to me. Or is there a curfew
for the Fat Lady to open the door from he inside?