The amount of time it takes to saddle a horse really depends on the individual horse, rider, and the skill level. If you are saddling a horse that has never been saddled it could take five min up to an hour possibly longer and a horse that is saddle broke will be saddled in the time frame of the rider.
Beginner riders will take longer to saddle than advanced riders and depending on the amount of time you spend grooming is a factor in this also. Make sure the saddle and bridal areas are clean and the rest is really up to the rider. If you are taking a lesson your time will be somewhat dictated by the instructor but if it is your own horse take as much time as you want.