I have a friend who is leasing a horse while in PT school. She's able to ride a few hours each week, but your mileage may vary depending on your classes and schedule. Alternatively, you could keep your horse at home for the 1st semester to get a feel for how much free time you would have to ride. That would also let you check out boarding barns if you decide to bring your horse the next semester (assuming you haven't done so already).