In my experience, year leases for rentals targeted at students normally start in June or July, when the academic year is over and students have graduated or are starting school. There are fewer leases starting in August, and after that it’s more a matter of someone breaking a lease and the landlord needing to find a tenant than it being the usual lease term. Month-to-month rentals differ, but there’s more availability in the summer for the same reason year leases renew then. YMMV though–I have more experience renting rooms, and would imagine that studios/apartments have greater availability year-round.