While defeating such a restriction is usually trivial, the point isn’t so much to stop you from using the app, as much as it is to make you aware of just how much time you’re spending on it. Sometimes being made aware of how much time you’re dedicating to a habit can help you in breaking it.

I know somebody who used a similar mechanism to quit smoking. He’d tally up each cigarette he’d have throughout the day, and having a number to reference helped to quantify the problem for him. Counting his smokes wasn’t what made him quit, but it helped him realize just how severe his problem was, so he was able to actually find the motivation to do something about it. Similarly, an app timer may trigger the thought of “I keep spending more time on this app than I promised myself I would, I need to figure out what keeps drawing me to do this”.