I did it recently. The first 60 odd miles up to Hartside pass is easy (reasonably flat with the exception of Whinlatter, which is pretty tame at a sedate pace with fresh legs). The last 40 miles down to the coast are the easiest miles of them all (even after the long day you’ll be flying). The bit in the middle however, hurts.
Hartside, followed by Garrigill, followed by Nenthead, followed by Allenheads…..by the time you get to Crawleyside you’ll want to cry. But when you get to the top you can smile again. Easy cruising for the remainder of the ride.
Took me 14 hours (12 hours riding time). That was keeping an average speed of about 13mph. Big averages are hard to hold in these hills, but theoretically if you started hard….the hills only form a small…ish part. It’s whether you can still manage the hills after that pace (they are as big as they come and stack up one after the other). I would advise starting early!