Seems like your store volume is similar to mine, as we are also switching to 4am from O/N. Odd that your just finding out about it. This would have been a decision that was made back in February, the end of the fiscal year, and is usually announced 8 weeks in advance. There is a transition process (4 weeks per corporate) that leads up to the actual switch. During this time your overnight team will practice as if they are coming in at 4am, meaning everything should be done by 2am if you guys start at 10pm. Pallets cannot be on the floor after 8, and really they want the floor cleared by 7:45 to prepare for store open. Certain areas of the store that normally would have been unloaded onto pallets off the truck and bowled out to aisles will instead be staged on flats or tubs at backside endcaps. Reason being, your team may not be able to finish all push by 8am, and no boxes can be on the floor after that time. Areas that are normally broke out into carts will most likely be left until all boxes on the floor are pushed. Eventually they will be expected to complete the entire truck by 8.
Now comes the bad part. If your store is anything like mine, everyone on flows hours will be cut significantly. The total number of hours stores will be given to finish their truck isn't changing, what will change is the number of team members that will be scheduled. If your store normally has say 20 flow members, expect 30 for a 4am process. Those aren't exact numbers, but you get the point. The idea is more people means the truck gets done sooner. It also means much shorter shifts for everyone.
Not sure how straight forward your stores management is. Many of our flow team members were led on to believe their hours wouldn't be reduced when the transition was first announced. But that was untrue, at least for my store. Our flow team members were just informed that there simply is no opportunities to work in other work centers after the truck push.