If you did 96 mile days at 12 miles an hour, that would mean 8 hours of riding per day. if you did 2 hours of stops , you could be away by 8:30am and finish each day by 6:30pm. That’d take 11.5 days, allowing 2.5 days for travel either end. Not a gentle pootle but not a route march either.
Otherwise 90 mile days to take 1/2 hour off each ride part of the day and take 12 days.
What we actually did isn't really relevant to the OP. We went a bit quicker than that and stopped a bit less and finished a bit earlier. I'm not sure what distances he did after I finished (exhausted) at York. If I was planning/organising it for myself I'd take longer. (But actually if I was planning it for myself I probably wouldn't do LEJOG at all, but that's neither here nor there).
As to the OP, who is beginning to plan, it would be a good idea to imagine what a
really great day would be like. How far, how will you feel at the end, what kind of lunch stops, how do you want to pass the evening and so on. Then you'll get an idea of what kind of places you want to pass through, where you want to stay, how far you want to do each day.
Then maybe do a bit of doom mongering and imagine a day with mechanical issues, bad weather, and so on.
We had everywhere booked in advance about 60% hotels, 40% friends' places. This left little room for replanning or contingencies, but fortunately all went well.