I would start by trying to find out what is causing it to be so slow:
Isolate the query in a separate application, so there are no other effects on it.
Time the query as is. If it is significantly different from teh your-app version, find out why.
Cut the query to the bone.
SELECT MONTH(StartUtc) FROM Employee WHERE Creditnumber='95A60378-0ECC-4D23-804F-71BB2BADED08'
If it is fast, keep adding bits of the query back until it is slow - then you can work on improving performance of the last bit you added.
Sorry, but you need to find out where your problem is, before you can fix it!