Yes, you can enroll in a course at any time, but if there are expected outcomes like peer assessment activities or due date for homework – and they have already passed – you would not be able to take part in them.

All the courses available on POK are scheduled to re-open several times a year. For most of them the new edition is launched right immediately after the end of the old one, for the others the new edition re-open after only a few weeks.