Instead of the TL giving up their weekend how about the ETL give up his and come do the ordering? Or the PA give up his Sunday to do the ordering? Or teach someone else how to do the ordering? There are plenty of options instead of trying to make the TL work on their weekend off.
I noticed you said the PA had another job on Sundays and ignored that because his other job has nothing to do with Target. He can have another job or he can have to baby sit or he can just want to sleep in late after playing pool until 5am. All of those hold equal weight when someone is not available to work, it does not matter the reason. The ETL is salary, looks like he better take his lazy ass in for those 2 hours and cover it then. The whole thing about asking for time off 2 weeks in advance works both ways, once it's posted that's what the schedule is. Perhaps you can work late that day and cover until 5:30!