Hi Nico, the time needed to export a video is afflicted by a lot of things : CPU, memory, duration, resolution, effects applied. The more things you apply to the clip (change original resolution, filtering, transitions, rescaling) the more time will be taken to export the file. Again, if you change extension a re-encoding process could be applied and I think this is the reason why you have to wait so much. To cut out time , first of all don't change resolution and original format, simply cut the parts you don't need ed export with original format. Once you got what you need, you can re-import and re-export the file in the format you need. Please note that a 50min. video in 4k may take a loooong time if you don't have an high-end computer (i9 at least).