IME - Save the Dates for weddings that aren't destination go out 6 months in advance for those guests that are out of town and will need to arrange travel. My girlfriend also sent them out to everyone in the wedding party, hosts, etc.
Invitations to the wedding itself usually go out 6-8 weeks before the wedding.
I've never been to a Friday evening wedding tho. Interested in seeing the responses. Lots of people don't seem to know what they are or how to use them. My SIL saw one on my fridge for a wedding I was in. She made a comment about not getting one which surprised me because when she got married it was like pulling teeth to get her to tell us when it was and we lived 12 hours away at the time.