I was in a slightly similar situation with my job.
My diabetic nurse is part time, and works 8.30-3 three days a week. I work full time 8:00 til 5:30, and there was an element of employer "grumpiness" shall we say, with regards to the first few appointments.
I was asked to arrange my appointments outside of work time, so I sat down and explained to my manager that it was impossible for me to do that because of the appointment times at my surgery. We came to the agreement that I can take my appointments, but to take an hour I have to give an hour.
Some employers seem to be scared when an employee is diagnosed with diabetes. The instantly think that we are going to take loads of time off and be off sick all the time.
All you can really do when they have this kind of attitude is work the time ahead of your appointment, and prove to them that diabetes isn't going to affect your ability to do your job.