Depends on the temp outside and how hot you load is. I don't shoot more than 3-4 rounds before letting it cool I let it cool for 10-20min depending how hot it is. It also depends if I am shooting to work up a load or just bangin.
If a gun has a good barrel, and bedded well, you can shoot as long as you want. But beware, too much hot barrel shooting, and it accelaterates throat wear.