It will depend on the course (some have additional elements which require additional length) as well as their timetabling and other factors.
Typically May is for exams. Last year we had two weeks of revision after the Easter break, this year it was before, so we finish earlier. The exams were all bunched in the first two weeks of the exam period as well. However, we have additional things to do to progress into the final year, so I need to stay around longer.
Late May is to be expected. They should give you a timetable of major term dates and the end of the course date. In reality, it may be sooner if exams are over quickly.
I would say you're classed as completing your year after you receive the grades for it and have no further results, resits or academic engagements to complete. So, mid-July, but it really isn't anything vital.