About 17mons. Engaged in April, married the next Sept.
My timing was based on the venue's availability, as I had one specific venue I wanted. Basically they had 2 dates available, June or Sept, and Sept was going to be better weather.
I dont think the actual time gap matters that much. As long as you have enough time to get your vendors booked, works with you and your FI and families schedules, that's all you need.