How early can you do online check in for a flight?

Question

I think it is 24 hours in advance max, but I am hoping there is a way to check in with more time until the flight (say, 48 hours?)

Answer 1

I believe it is 24 hours in advance.  Though it depends on the airlines, best way to check is to go online to the airlines website and click on a tab for check in, from there it will give you the details.  

Answer 2

depends on the operator. I fly ryanair alot its up to 6 days with them, and no later than 4 hours before.

Answer 3

I know United is 24 hours.  And the sooner the better.  If you are the last one to check in, you may get bumped in an oversold situation.