Rolex does not engrave the case back. If it says 24 hours at Daytona, or wording like that, the watch is not real... It's a fake, or as we say more kindly.. It's a replica, and can be bought on any replica watch web site for $30 to $80, for an automatic mov't., 21J, made in China.
Also, the sub-dials will not function on this watch. A Daytona needs the proper movement to operate the chronograph as it was intended..... To act as a stopwatch.. and measure time... seconds, minutes and hours. This is done by activating pushers at 2 and 4 positions, and the pushers on 21J replicas just don't operate a chron. for the purpose of measuring time. They may move and measure something else, like military time, or the date, but definitely not record seconds, minutes or hours.
There are also no manuals on how to operate the Daytona that comes with these replica watches. You should know how this watch functions and how to operate the pushers, and what they do before you should buy and enjoy this type of chronograph watch. It's simple, just take the time to ask people in the know... how the daytona works, what the sub-dials measure and how to use them, etc. In no time you'll understand the operation of this beautifully made watch. Unfortunately, a daytona is out of reach for most of us... That's why seeking out a quality rolex replica for much less money is the way to go if you love this watch... A quality one can look, feel, and function just as good as the authentic Daytona, and you won't have to out out over $10K to get one.