As day walks go, this one is the daddy, and it's worth doing just to be able to say you have. I know people who do it three or four times a year and can't wait to get back and do it again. Each to their own I guess
If you can get mid week out of school holiday periods you will have far fewer people around. Saturdays in the summer tends to be charity walk season (BT had 65 teams of 4 out the day we did it) and can be pretty crowded.
If you have 2 days to spare then it makes for a great 2 day walk.
Base yourself at the Station Inn and Ribblehead (either B&B or camping barn). On day 1 go from there, over Whernside and up Ingleborough. Then, instead of the path back to Horton, take the first path off the summit plateau which takes you over Simon Fell and Park Fell, and back down to Ribblehead again. It's roughly 15 miles, give or take, and a cracking good walk.
Then enjoy a meal (stayed there three times now and can't fault the food), couple of pints (excellent Black Sheep Ale there), good nights sleep and breakfast (which you can book if in Camping barn as well as in B&B).
On the second day, hop on the train from Ribblehead (station is opposite the pub) down to Horton. From there go over Pen Y Gent and back to Ribblehead (about 10 miles I think). The new route avoids the bogs so much easier going and the paths are clear and good underfoot.
You get to do the full Y3P route without the physical extremes of doing it all in one day