Ciao Fdell, I understand your questions partly, most of all, I don't understand whether you already stayed in Florence and are only now, after your stay, trying to communicate your license plate to the hotel? Or are you preparing your visit and wondering how the system works?
So I'll address both points.
1. If you haven't yet been to Florence, then rest assured all you need to do is, when you arrive at the hotel to check-in, tell the staff at the hotel reception that you drove in to get to them and give them the license plate right there and then, wait for them to give you confirmation it has been sent to the local authorities and the license number has been registered on the white list. They have software to send the license plate number to the authorities and they cannot communicate the license plate ahead of time before your arrival, it has to be within a specific time frame from the time you enter the ZTL to get to them. So AFTER you pass through into the ZTL, they communicate the number to have it taken off the list of plates that have been registered. The cameras register all license plates going in, they register to have you "taken off".
2. If you already stayed at the hotel in Florence and you gave them your license plate but aren't sure they registered it and communicated it to the authorities, all you can do is wait. I am not sure whether they can check the numbers they send in every day, once your day has passed. It might be months if not a whole year before you get the fine, if the plate was not registered to be taken off the list of those that entered the ZTL on that day.
Keep the receipt or anything else you have that proves you stayed at the hotel in the ZTL area, so that when you get the ticket you can contest the fine. You can most definitely show them you stayed in a hotel in the ZTL and claim it was the hotel who failed to communicate the license plate.
--> If you stayed and forgot to give the hotel the license plate at the time you arrived, you can understand the hotel cannot and will not be able to add your license plate after the fact. They are only given a few hours after you've entered the ZTL to get to the hotel to add the license plate to the registry. So if this were to be the case, I am sorry to say you will still have to wait and see whether you get a fine and then only after try to contest it, by showing you stayed at that hotel. Also be aware that if you were in a rental car, the rental car agency will charge you (they have your credit card on record) an administrative fee for having to track who had the car on the date and time the car entered into the ZTL and having had to give that info to the local police -- so if you see this on your credit card, then you know the fine is on the way.
Let me know if you have any other questions or doubts, I'll try to help as best as I can.
