Any travelled with jet2 from Blackpool?

[TittyBojangles]

How late can I get away with getting to the airport if we check in online?

Don't be fooled by online check in. You still have to stand and wait in the check in queue. The online check -in is just a cheap way for jet2 not to print boarding passes.
We fly with jet2 every year from Manchester and up until last year we checked in online. Last year we weren't allowed to as we had a 7 month old and there was absolutely no difference in the check in procedures - just you print your own boarding pass (A4 piece of paper).
Hope this is helpful. I would still allow 2 hours.

Balls, was hoping we could get away with leaving it a bit later, also presuming there won't be the same queue issues at Blackpool.

What time is your flight - early morning, is that why you are wanting to get there later? Are you stopping over at a hotel?

Our flights are always early morning (6:35am this year!) and we stop over at the Radisson Blu otherwise we would have to leave home at 2:30am to get there for 4:30am!!! It allows us to have 'an extra day' of our holiday.

Can't remember exact flight time, about 730 ish I think. Not staying over as live only about half an hour away. Just want to avoid a grumpy, tired ds on the flight as much as poss. My mum and dad are travelling the the airport separately so can get there earlier/save us a place in the queue if needs be.