You’re going to get the dreaded “It depends.”
According to the Academy of Motion Picture Arts and Sciences and
the British Film Institute a feature is a running time of 40
minutes or longer. The screen Actors Guild defines feature length
as 80 minutes.
Festivals are all over the place.
Distributors usually want at least 80 minutes, but that, too
depends on the distributor.
And remember that the one page/one minute guideline isn't
set in stone. You're final movie may be much shorter if it's
mostly dialogue or if you cut a scene that doesn't work. And it
might be much longer if you have a six minute car chase that
takes up 3/8's page.