There will not be another time where you will likely be living, working, relaxing, exercising, eating, thinking and socializing with one group of people. This means that there will never be another group of Non-Christians who will be able to observe your life at such close quarters, and with whom you will have such incredible opportunities for multiple conversations about the gospel.
Just think about this for a moment: once you graduate you will have various different groups of people whom you might seek to evangelise: your colleagues, your neighbours, your sports teams / interest groups, the people who eat in the same restaurants you do. I could go on. But while you are at College these might all be the same people.
This means you will be more observed that anyone else. It is quite possible to choose to hide parts of your life from colleagues, neighbours, sports teams, etc. It becomes hard to do so if they are all the same interconnected group of people. People will observe whether you are living for different things in a different way to every other student.
All this leads to many opportunities for gospel conversations, and for ongoing dialogue about the gospel.