There is no chance anyone outside of the Top 20 will be doing a six hour bike split, FFS 
I’m looking at 6.5hrs, on a good day, so am preparing myself for a solid 7 hours in the saddle if it’s raining or wet.
ETA: Looks like less than 20 people rode under 6 hours in 2019.
Now I know the course is different, but it’s pretty similar.
EATA: @Chriswim is a monster and rode a 6:16
He rode a 1:52 at Helvellyn, whereas I rode a crappy 2:08…which was massively weather affected 
As that was 60km, I’d look to be 48 minutes slower than he was over 180km 
Hence the 7 hour tops estimate 