I studied Mechanical Engineering at Uni and even with a fairly demanding schedule there is plenty of free time for other things. Also it depends on how you choose to study. There are two main options, 1. Keep up with your notes and reading during the year or 2. Work harder than you have ever worked in your life in the 3 weeks leading up to exams. Both are good options. Option 2 gives you more free time during term.
As for free time outside of term time, every year we were finished our exams by the end of May and didn't start term till the end of September plus there was about a month at Christmas and Easter so there is plenty of time to devote to other things.
My university had a Mechatronics course and some of their students incorporated RC into their final year projects. Even on my course one of the projects available was to create a flight simulation using an RC helicopter connected to a support rig. Although apparently the first year the project was run the student spent all of his time building the helicopter and barely passed.
So if you are doing an engineering degree there are plenty of options to incorporate the hobby as you progress in the department. One final thing I'd say is make a conscious effort to make the most of your time at University and get involved in anything that you are even remotely interested in through societies or whatever. The time goes by so fast that if you blink you'll have missed it and before you know it you'll be in the rat race longing for those carefree student days.
Oh and one other story. My friend Will spent his student loan on a Tamiya Subaru Impreza and was really proud when he finished it. Then his girlfriend drove it into a kerb and damaged the suspension. That pretty much sums up student days.
