Does anybody know of any home-made, small, timed, automatic, or any other kind of release mechanism? I have tried and tried to look for some good ones but they are all either expensive or large(er) than i need them.
Thx.

try a micro servo and a linkage through a small tube in which a rod could slide through..

Have you looked at the Texas timers the free flight guys use on their outdoor duration planes? They tend to be small simple and work well.