The time for invitations to be sent out about 3 months time so that your guests do have time to book the hotel rooms and travel plans arrangements. I know I had sent out 9 months prior to which most of the family had made plans for the tickets and reservations booking. The RSVP can be 4-6 weeks prior to the date for the final count. One piece of advise would be to add attire wear if you have in mind for your guests to know what to expect.
Most Indian invitations do have formal wear or black tie to have guests prepared for their packing ahead of time.
We sent ours out already. We know hotel prices will only go up and people are trying to plan their summers (wedding is August 13). We also wanted to give our large amount of out of province guests time to look for flights as well.
How much time does your venue need you to give your numbers? Typically, it ranges from 3-6 weeks prior to the wedding. From there, add a week prior to act as the RSVP deadline so you can tidy up the info for the venue. You can send the invite 4-6 weeks prior to that.
You can send a Save the Date to out-of-towners so they can get a head start on travel arrangements and accommodations.