Park literature regularly refers to 93 miles. So apparently no one knows the precise mileage. It depends on your conditioning and your objectives. Nine-day trips seem popular. I would suggest at least 10.
Trail runners can travel the distance in three or four days.
Most guidebooks launch you from Longmire. Along with Sunrise, parking and security are best here. Longmire and Sunrise are also the trail's handiest resupply points. Either direction has its rewards and drawbacks. Traveling counter-clockwise, as I did, kept the mountain in front of me as I approached Indian Bar on the east side, and when I labored my way up to dazzling Emerald Ridge on the west.