filipetolhuizen nailed it. Somehow I had mistakenly assigned the dynamic instead of the normal core. The dynamic core causes the crash after ~7 minutes, under the normal core the problem does not occur.

Thanks!

The dynamic core gives the best performance, but it's still not 100% under a few games, specially simple ones. It crashes DOSBox after 5 seconds upon launching Cartooners. The Windows 3.x version of Nitemare 3D works fine under XP 32 bits, you just can't switch to full screen mode or it'll lock-up, but you can adjust the window size. Music will play using the selected windows midi device.