Assuming that the rate that you used doesn't have any minimum duration requirements, if you return at 2 days you will be charged for 2 days.

Just keep in mind that if you return the car more than 48 hours and 30 minutes past the original rental time you will then be charged the hourly rate for the 3rd day. After 2 extra hours you would then be charged for the full 3rd day since that would be less than or equal to the hourly rate for the extra hours.