Totally depends on which school you are going to. I went to Gustavus in the 90's which runs a pretty intense program. They carry 30 players and the time commitment for the top guys is similar to d1. We traveled a ton, from February to mid-May we had matches every weekend. The spring season was short ending in mid-October. During the off-season guys played tournaments, and practiced on their own. The challenge matches were as intense as the real ones. Don't forget that your coaches will have a huge impact on your experience. I had an awesome coach who would have done anything for you on or off the court. I am in my mid-30's and an a coach now, not for a school, but a teaching pro.
d3 tennis IMO is playing at higher level than ever, it's a lot deeper. I recommend a website called Divsion3Tennis.com. It's updated regularly, and if you read it, you'll be an expert on d3tennis nationally.
If your school is not competing nationally, you can still have a great experience...it's really what d3 is all about...having fun, learning about yourself, traveling, making lifelong friends. Some of my best friends now are guys from the team...and guys from other schools too. I am playing a former teammate tomorrow morning...and it's gonna be a war
...best of luck