If you have a flight at 6am, you need to be listed for 2 flights the night before that there is a reasonable chance that you will get on. That is it.

If there is a 6pm and an 8pm the night before, you need to be listed on those with seats available 24 hours before. So, just list for the flights a few days our. Check the status of seats the day before. If there are seats, and you still miss both of those, you are covered.

Or, just do what everyone else does. List for one flight. If you don't make it, call in sick.