The main difference between IOP and OP is the time required in the program. The offered activities and groups are often the same; you’ll just do more of them in IOP than in OP. IOPs typically require attendance at least 3-5 days a week for 2-4 hours a day. Our Outpatient Programs at Drexel are didactic lectures and focuses more on internal processes. They are typically scheduled 2-3 days a week for 1-3 hours.