if you going to a sixth form (as in it's part of a high school), you are most likely going to have full time, as in from 8:30 - 3:00. you will usually have only one lesson per subject per day, but sometimes, especially with classes that don't have a lot of students, you will be on a reduced time table, i.e only 3 lessons per week as opposed to 5. sometimes you may have doubles. since you are doing 4 subjects, you'll most likely have only 1 free per day.
as for colleges, some colleges do a morning and afternoon timetables. so your lessons might actually start at 12:30 or so, but end at 4:30. or start at 8:30 and end at 12:30. you'll probs have a lot free time,