I know that it was very different for a lot of groups, but for me, I would meet with my mentor every day for about 2-3 hours or so. So on average I spent about 12 hours a week with my mentor. I did not receive a lot of work to do outside of our meetings, just a couple of things here and there, so the workload was not too crazy; however, if that is something you were looking for, it is very easy to simply just ask your mentor for more things to do. For my project specifically (I was doing a CSE research track), I worked almost only with my other interns and rarely did stuff on my own, so it was a very collaborative environment.