First thoughts -
Your six hours is completion time and includes your pulse down and hold times (20 min max to reach pulse at the hold and end, hold time depends on various ride/day specific factors but is typically 30-40 min, and your final presentation to the vet at 30 min after crossing the finish (this includes the pulse down 20) - so up to an hour and a half, leaving you 4 1/2 hours saddle time. A 6mph pace will easily see you finish within the time.
On the rides I have done (several 12s, two and a half 25s) there were water stops every 3-4 miles. This breaks up the ride as you might sponge your horse, or give them electrolytes, or a snack, eat or drink yourself, etc. What you do when is ride environment and horse specific and your first rides are experiments in finding what you and your horse need to be successful.
I don’t know what your 8 mile ride pace is like, but I personally find walking for a couple of hours more tiring than any 12 mile Endurance ride I’ve done. It’s much easier for me to do walk/trot with somewhere around 25-40% walk (the longer the ride the lower the walk %). I did a 13 mile night training ride last September. I did a 12 mile Saturday, the 13 mile training ride Saturday night (7-10:30pm), and another 12 mile on Sunday. The two 12 mile rides had mid point vet checks and holds, but the 13 mile training ride just had a pulse check at the midpoint water. Even that dismount for ten minutes was enough of a break that I had no trouble doing the 13 miles - and we were moving out in trot much of the time.
My 25 mile rides each had a mid point hold (12-13miles). On those rides I was dismounting and giving my horse electrolytes at the halfway trough. On the hot rides I dismounted and sponged at every trough. Water is often a point at which riders catch up and I was thinking about trying to get ahead of some riders, or keeping my horse calm as we hung back.
In between these breaks much attention is on watching for the ribbons, remembering the trail talk, thinking about how my horse is doing and encouraging him (he’s still learning too - we’re new at this game). Realizing I haven’t seen my ribbon colour in a bit, debate going back to check, etc. I admire the scenery and notice how it’s different from other places I’ve ridden. I’ve thought about gear, both new (what size and style of saddle bag will suit my needs) and old (my traditional 1" wide stirrup leathers tenderized my knees on my first 25). Coming into the hold I’m thinking about what I need to do to get his pulse down, and what I need to do before we go out again, and what time I should tack up. On the half 25 I was thinking about my horse (he was tired) and if I should quit, and if I did should I call for pick up, and what I could do to help him. I did quit about three miles before the hold, opted to hand walk back to camp (regretted that btw, but I’d thought we were closer), and paused for grass whenever we found some.
I rode with other people on some rides - by plan and by chance - so we’re chatting a bit, discussing our horse’s needs at the water, and such. The rides I’ve been to people have been able to ask if there’s someone they can ride with, and there’s always been someone willing to buddy up, even if it’s just for part of the ride. I also rode with someone who just happened to be heading out at the same time (staggered start) and our horses got on well so we stayed together. I have been both the newbie and the guide and there was a lot of talk about the sport, strategy, process, experience, etc.
I enjoy being alone on trail with my horse generally. I haven’t been bored yet!