Exactly the same as with a paper ticket. Occasionally the e-ticket isn't set up right and cannot be found, so you should take your IATA ticket number with you to the airport (the ticket number is normally on the receipt that you were emailed when you bought the ticket). They can always find it with the ticket number, remember to have that with you. Checkin time varies by class, but 2 hours is typical and enough. I've made flights with less than 30 minutes to departure time, but that was in F and required an escort through security. Don't recommend much less than 2 hours for check-in.