Certified GKH Gardening Expert
That depends on the conditions that it is in. If it dries out fast, then it will need watering frequently. If it does not, then it will be longer in between waterings.
A general rule is to only water once the top 2 inches of soil are bone dry. Personally, I like to wait longer for these flowers, since they prefer dry, rocky, and sandy soils.
This article will give you information on their care: https://www.gardeningknowhow.com/ornamental/flowers/portulaca/portulaca-plants.htm