If someone arrives the night before they are scheduled to check in. Say they ended up on an earlier flight or the most economical flight arrived the night before.
Can that person still use ME even though their reservation technically wont start till the next day? Would it matter if they took the ME after midnight?
Can that person store their luggage with bell service till the next morning?
Can that person "hangout" at the hotel lobby till the next morning. At which point they can simply go to a park.
NO, you can not take DME unless you have an active reservation...and that doesn't mean a reservation that starts the next day.
I would be very unhappy if I walked through my resort lobby and found someone was spending the night there!! So yes, I would hope that person would be told to leave.
DME does, in fact, run 24/7. If they know a guest is arriving at 1am, there will be transportation for that person to their WDW resort. No, DME won't pick up the bags and deliver them to the resort. The guest will have to get their own baggage at baggage claim and bring it to the bus with them. But there will be a bus/van to get them to their resort.
If you get a cheaper flight, the day before your reservation? You have a few choices.
1. stay the night at a hotel close to the airport. Get your bags when you arrive, bring them with you to the resort. then, return to the airport in the morning, go directly to DME and take the bus to your resort. You can do this as early as you want.
or...
2. book a stay at a value resort. You can then take DME to that resort. If you arrive prior to 10pm, you can tag your checked bags and DME will get them to the resort. BUT...you will have to get to the new resort the next day. You can take a cab, with your luggage, to the next resort. Or you can head to a park, from the value resort, have Disney transfer your bags to the new resort, and then head to the new resort around midday, from the park, and get checked in.
But no, you can't use DME the day before your reservation starts. No, you can't spend the night in the resort lobby.