My solo run took 100+ hours. Co-op runs tend to be slower. The game has three acts, as a rough estimate you can say each act is the same length. (This will vary wildly, act 2 can be very short and act 3 can be very long, act 1 can also be the longest as you’re still learning the game.)
If you’re not sure what act you’re in, you’re probably still in act 1.
If you can give details of what you’re up to, I can tell you more definitely.