actually we don't run A/C overnight (we do keep the heat ON big time though, but even stores that close do that as well). Also, 2 ETLs is optional, some overnight stores have their replenishment position fulfilled by a senior team lead instead of another ETL. In terms of cost, yes its true most overnight stores have more staff, more people, but its only for the purpose of processing more stock. While most 4am store have 3-4 trailers a week, we take 6-7 trailers a week, and each trailer is FULL (1950+20 pipos, to 3200 with no pipos). Honestly, if we had to do this during the day, while the store is open, we would have to fill the entire backroom with flatbeds, the line, each aisle of receiving, and probably the FIRE TUNNEL, and it would take twice as much in flow labor.
Where the O/N process rack up cost actually isn't on the overnight shift itself, but on things that bleed into dayside labor. for instance, our backroom closer every night has to prep the backroom and receiving to unload the trailer and pull the autofills, a process which is ignored every other night at 4am stores. Also on the morning shift we have to allocate extra labor... with no flow TMs around we have to schedule at least 10 people each morning to make sure we have backup cashiers and at least 1 person on the salesfloor to help guests. We wouldn't need any of them if the flow team was there when the store was open.
So in terms of the "Vibe" affecting your team, believe you me, that is the intention. The whole point of having a 4am or 6am store is so that you don't have to staff the store while the flow team is there.