When is the best time to dispatch my invitations?

We sent out save the data about 8 months before so people could mark their calendars, and then sent out invites 3 months before so that it would be close enough most people would know what they're doing at that point and not forget to RSVP while they're waiting to confirm plans. We did still have to chase a few people down for their RSVPs though lol.

This can vary depending on your guests, we had a lot of out-of-towners coming in so we gave them 4 months notice so they had ample time to make arrangements. If it is something a lot of people will need to plan for, give them lots of time then send an rsvp reminder closer to the date for the stragglers.

Usually it goes by when you need final numbers for your vendors. Which is usually a week before (some places wants it two weeks, or even a month). But you also want to give yourself some time, are you doing a seating chart that needs to be made? Or even place cards?

For example, my venue needed final numbers for the dinner and drinks, I also needed final numbers for rentals in our ceremony location for chairs so every one can sit and I was getting place cards done. So to make sure that I was able to order my place cards in time and change any rentals last minute with out a huge surcharge I wanted my final numbers in a month before the wedding - so July 18th. I sent out save the dates a year in advance because it was considered a destination wedding, so I sent my invites out the first week of May for local and mailed out the last week of April for those that needed it to be mailed.

For your March wedding, this is tricky because you don't want to send invites during Christmas week. I would suggest mailing them out the first week of December (gotta keep in mind the delays) since you did not send save the dates and you do not want them mixed up in lost mail around the holidays - it is crazy and happens more often than you think!
Hope this helps