Another vote for taking two days for Manchester to Hull.
Seems to me time taken on long rides varies, often for no apparent reason.
I've done York Humber Bridge York (similar distance) in 10ish hours, but equally some attempts at that ride have taken a lot longer.
Touring is a state of mind, riders may want to stop several times to take pics or have a swift look at attractions they pass.
To get across in 10 hours, I reckon you as leader would have to crack the whip.
Is this the type of ride on which you want to constantly badger people to get moving/get a move on?
Then there's the obvious 'barring mechanicals' or just as likely, minor routing fail.
It all adds up to two days - if you want a relaxed, touring experience.