The movie was on in the early 1990s on TV all the time. It was probably from the eighties though. Its about a guy who opens a medicine cabinet and there is a huge black hole or tunnell like thing behind it. And there are these monsters that only come out at a certain time every night.

The only movies I know that sound like that are Indian in the cupboard and
Monsters, Inc.

You might be thinking of the movie "HOUSE" the fist movie, since I think there's like 3 total. I have the 1-2. I love the 2nd one. Here's a link, this is the only one I could find wit pictures.. but YouTube should have parts of the movie too.. The 80s Movies Rewind « -- Home of '80s Retro Movies