Unfortunately there are 86400 timestamps per day, so enumerating this across all days and all devices would take forever. Instead we'll use a heuristic: we'll

Unfortunately there are 86400 timestamps per day, so enumerating this across all days and all devices would take forever. Instead we'll use a heuristic: we'll start with the last screenshot and subtract one second at a time, downloading from each and seeing if we get a valid photo or the error XML that comes up if no screenshot was taken at that second. If we get the error XML 20 times in a row, we'll assume the recording is over and give up. Binary search?