By hydration, I’m assuming you are referring to curing of freshly placed concrete. A minimum of 7 days of continuous wet curing is recommended. Continuous means the exposed concrete surface is wet the entire duration. Not just “watered” twice a day as has sometimes been suggested by contractors. Use of a spray-on curing membrane is an option if for some reason water curing is not practical.
If you are looking specifically at swimming pools, this ASA Pool and Recreational Shotcrete Committee Position Statement “Curing of Shotcrete for Swimming Pools” provides more details: shotcrete.org/wp-content/uploads/2022/01/218216_ SCMSummer21_PS7v2.pdf Also, for a more detailed look at curing, the American Concrete Institute (ACI) document, ACI PRC-308-16 Guide to External Curing of Concrete is an excellent reference.
You can find this at ACI’s bookstore (concrete.org/store.aspx). Finally, a good reference on the basics of concrete, from materials to placement and curing, is the Portland Cement Association’s “Design and Control of Concrete Mixtures, 17th Edition.” You can find this on the PCA website bookstore.