Regardless of how long you've played or how many jackpots you've hit, you can reasonably expect about four or five royals in your next 400 hours of play. Of course if you play faster or slower than 500 games per hour, your average playing time per jackpot will be shorter or longer, respectively.
How Fast Do You Play?
To measure your own rate of play, first build up some credits on a machine. Then check the starting time on your watch, and drop one quarter into a cup as you make each play. After counting 40 games by dropping a full roll into the cup, check the time, subtract the starting time, and divide 40 by the elapsed time.
For example, if it takes five minutes and 20 seconds (5.33 minutes) to play 40 hands, you are playing at the average rate of 40 + 5.33 = 7.5 games per minute. Multiplying by 60 yields a speed of 450 hands per hour.
Be sure to play at your normal pace when timing yourself; if you try to play fast, you will not only get a false indication of your rate but you also may make costly errors along the way. Better yet, get someone else to time you.