Save the dates and invites

Save the dates are sent out 6-12 months before the wedding. Invites are sent out 6-8 weeks before. The replies are due back a couple weeks before your venue/caterer need a final count and gives you time to track down anyone who didn't respond...generally 3 weeks before the wedding.

The timeline depends on the crowd - is everyone local or do you have a significant number traveling in from out-of-town? If you're all local, then you can do 3 months for STDs, 6-8 weeks for invites, and reply by 3ish weeks ahead of time. If you have a lot of OOT guests, then you can do 6 months for STDs, 8-12 weeks for invites, and the same reply dates. There really is no "set rules," but I wouldn't do earlier than these because it becomes too spread out.

Save the dates are generally sent out 8-6 months prior to the wedding and invites are normally sent out 8-6 weeks prior to the wedding with an rsvp date 2-3 weeks before the wedding. This will give you time to reach out to those that don't reply, give your caterer your final guest count, and create your seating chart/escort cards.