Depending on the conditions this can take between 2-6 hours to dry. On hot dry days you can walk on it right away. It can take just over an hour to completely dry and remove any changes of tracking foot prints into it. However on a humid moist day it can take you the better part of a day to completely dry.
This answer depends mostly on the materials you use to seal your patio with. A water based sealer will require sealing sooner than a patio sealed with a solvent base sealer. With a water based sealer you may need to seal every 2 years. A well applied solvent based sealer can go as much as 5 years under ideal conditions.