Hi,
deleting files can be very long specially with Guttmann and the hard drive works very hard. So when you want to do anything else, it's very long as well. You should add the "stop" and "resume" buttons in the deleting files box. So when you want to work you can stop the task and resume it without starting all again.
Cheers,
Mon

The problem with that is that the list of deleted files is a moving base, so that it won't necessarily represent the state of the disk when you return to the task. I know you can scan in one window and do some other work and return to the Recuva window later: I don't know what file status validity checking Recuva does.

You could speed up your task dramatically, by a factor of 34 in fact, by just using one pass to overwrite data. The reason why has been discussed on this forum many times, or you could spend ten minutes on Google or Wikipedia.