So I’ll be in California for only one day but I really want to visit UCLA, USC and Pepperdine and I was wondering if that is at all possible? My friend visited UCLA and USC last summer in one day but she said I probably won’t make it to Pepperdine… do they have anything early in the morning or later in the evening? I really want to visit all three. 
Check their website – they should have a schedule up of when tours/information sessions are. It’s also possible that they might allow self-guided tours.
That being said, I personally don’t think it’s a great idea to cram many tours into one day. I found that it can be hard to keep schools straight when you’re visiting them one after another, as well as being a generally exhausting experience.
Maybe you can see the campus but not the tour. My family did Pomona, USC, UCLA in one day, iirc. Very early tour of Pomona to see the students on the first day, then off to USC for a real campus tour, after lunch we went yo UCLA for a real campus tour.
Hmmn, I take it you are not familiar with LA and its very distinct traffic patterns, e.g. hell on earth?? While it is potentially doable, it depends if you are doing a scheduled tour, and I would say to assign, at least, 2-3 hours, per university. So, that comes out to about 8-9 hours just on campus. Your traveling time between each campus, depending on the time of day (and this is very crucial) will be potentially 20-45 minutes from USC to UCLA, but from UCLA to Pepperdine, it could range from 40 to 90 minutes. So, your day will end up (and this is provided all your tours line up) being closer to 10-11 hours.
All in all, I would not recommend doing all in one day, between the traveling and all the things you should be looking out for, I think you really dilute the purpose.