I would like to make an early fall 2018 trip to London with a side trip to Cambridge. I have tried to check the schedule for King's College but am still not sure whether I have to wait until the term starts, or whether there are evensong services earlier than that. I think the term starts October 2. Also wonder if some of the other colleges have strong music traditions and offer performances on a different schedule. It appears that St. John's College also has good offerings for musical performances.
I don’t have a definite answer to your question, but my guess is that any of the colleges are going to follow the academic calendar. A local church is much more likely to offer daily evensong services, independent of the colleges’ schedules.
It would be best to check on the college website: www.kings.cam.ac.uk
The guide to choral services (http://www.kings.cam.ac.uk/chapel/choral-services) lists services up to July 8 and notes that choral services start again on September 22.