Laura B , you don't have to check in at the original time if you have received a text from airline before check in time telling you to check in at a later time, this happened to us a few weeks ago, we were delayed 4 hours going to Minorca and received a text just as we got up at a hotel at gatwick airport, so e went back to bed
the text said to check in at a later time, you just have to make sure you have the correct details so you don't miss the flight.