london gatwick offer a 'twilight' check in, which is what you mention-the flights before 8.30am you can check in from 8pm the night before. I wouldnt worry about that.
the other 1 you mention-60 days before hand, is the online check in, print off own boarding pass. It is very easy to do, and means you can buy pass check in at the airport if hand luggage only.
if you are worried then just check in at the airport as normal-easyjet don't charge for airport check in and it might keep your mind at rest.