The short answer is it's going to depend on what job you do. At the moment I'm lucky if I get to play tennis any other time except weekends and then if I get two hours I'm doing well.
The other thing to consider is that court access etc...is going to be more expensive during the times you are free i.e. evenings and weekends. Especially during winter when covered space is at a premium (depending on where you live of course).
If you work 9-5 I reckon you can fit in an hour or two say 2-3 times a week after work and a good session at weekends. This is what you can probably get done initially.
The second factor is the spouse/girlfriend/DIY factor. The more you go down that road the less "you" time you get. Unless you have a very understanding spouse and the money to get someone else to fix your place up then you will find that weekends are not the 10hr a day free time paradise they used to be
...That and evenings you will want to spend some time together, or with your friends etc...
I won't go into kids yet as you are still in college but once that avenue opens up you can scratch a whole bunch more of "you" time.
I reckon straight out of college you should be able to manage 3 evening sessions and one weekend session a week. Enjoy it while it lasts!!