The two hotel’s I have been in recently use NFC tech but seem to use a “proper” way of storing checkin/checkout times, I haven’t been able to clone it using my Android device, I need to get my hands on a ProxMark to try some things.
Do you know what frequency the HID iClass uses? It sounds like it’s 125khz but might be worth getting a DangerousThings diagnostic card to check.