In the spirit of that exercise, the fixes should not take an excessive amount of time to review. If they are, it's likely either the scope of the fix is too large for that kind of exercise, or the PR review process is too in-depth.
I would also question why only 3 of 8 devs approve PRs. Even if that can't change more broadly all of the time, this kind of exercise seems like a perfect time to allow everyone to review PRs - two fold benefit, more fixes are reviewed and gives experience reviewing to others that don't get to do that regularly.
So yes, definitely still do PRs, and if that is problematic, consider whether that is an indication the PR process may itself need to be reviewed.