It’s not healthy, no. Having an erection that won’t go down is called ‘priapism’ and it’s not good for you. Cocks get hard by restricting the blood flow OUT of the penis, so if you have an erection for super long without any respite (2 hours or more) then it can start to cause some serious problems. And trust me, you don’t even want to READ what they do to get it back down, let alone have it done to you.
So yeah, don’t use cock rings for too long to try to do this, and don’t take too many blue pills either, or you’ll end up in ER with very unpleasant things being done to you.