I found my review, we were on a scheduled British Airways flight leaving Heathrow at 7.05am. This was in 2016, I'm sure in 2013 we were on a BA charter from Heathrow to Rome but I can't find the times for that. It was fine.
Hopefully someone who has actually flown from Manchester will be along with some useful information soon.
Have you actually done this journey? The OP was asking for first hand experience not wild guesses !
I've only done the flight from Heathrow to Rome, it's been a while but we certainly didn't fly at 4am. I'll see if I can find my posts.
Yes, it's a shame the OP didn't join before their cruise. They could have had lots of their questions answered and might have had a better idea what to expect.