Mating moths - Owlet Moth - Noctuidae sp

These mating moths were almost invisible aaginst their background of paving stones.
They mated for almost two hours before it got too dark for me to see them any longer but they were gone in the morning.

Now I have two questions:

1. How long did they mate for?
2. They cannot see themselves, so how do they know they blend in with their background and are almost invisible?