This mainly depends on where you will be using your engagement session photos
Most couples utilize the photos for the save the dates
General rule of thumb is to send save the dates 6 months before the wedding
Local weddings 4 months in advance
Destination weddings 8 to 12 months in advance
Engagement sessions should be 1-2 months prior to sending out your save the dates
This provides you time for the images to be edited, select the images, design the save the dates, order and have them sent out