I'm doing MAX OT right w/a five day weight lifting split (Monday-Friday). I am currently doing cardio about 3 times a week, on Monday, Thursday, and Saturday. I was thinking of adding another cardio session on Sunday, but that would mean that I don't have any day during the week that is totally dedicated to rest. Is this a bad idea? Should I stick the fourth cardio session somewhere else on one of my weight lifting days that way I can have at least one complete day of rest a week?

yeah man... try and get it (cardio) if you can on your least intense weight lifting day... and if this is going to be the case make sure its somewhere between 5 to 7 hours apart... perferbly 7.

i assume you are cutting. depending on how fast you would like to loose the fat... and if you are not an ectomorph body type... you can benefit from more cardio. dont in any case whatsoever neglect a day of rest. this is important. 3 days of cardio is fine... but again... if you can fit in another day and it proves beneficial for you and you arent loosing too much muscle then go for it.

i do around 5 to 6 cardio workouts a week. im a meso-endo body type... i can easily build and maintian muscle. i can afford all that cardio provided im concentrating on my muscles on lifting days.

What kind of cardio is this? Interval? Moderate/ light? How long have you been exercising? I think you'll be safe. Just don't run or do one activity in all sessions.