Seems kind of excessive, as others have pointed out, it takes very little time to change into pants. When you get home from work, pick out a pair of pants and put them next to your bed. That way, in the morning, you can change your pants while still in bed, if that makes it easier. I think people would notice the PJ's and some folks would likely judge you for wearing them to class. I think it comes across as sloppy and careless, whether or not that is true. You seem to be looking at it from a practical, time-saving perspective, but other people won't know that by looking at you.