I agree with Scott and Casey, BJJ does not translate well. However, a way to get mat time is by drilling techniques and not rolling. Assuming you have the time to drill and complete your normal training sessions.
This week I am scheduled for twelve hours of training, BJJ account for two hours. However, I am getting 5 hours of mat time by drilling techniques. I can get an hour of drilling in per day, which will not affect my fitness, as long as I do not free roll. When I roll my heart rate gets into the anaerobic zone, without accounting for this, would ruin future workouts. Thus they need to be planned. You will know what your body is able to get away with.
Good luck.