Well, that isn't what I'd use, but after a day, it should be cured enough. All cement products reach their stated strength in 28-days, but reach probably 70% in the first day or so. The load on it isn't very much per square in, so it should be fine. Adding more water than stated, doesn't change the cure rate, but does affect the strength. Not enough, and it can't create all the bonds it should.
The mixture doesn't 'dry', it gets chemically combined with the cement. Excess messes up the matrix, too little, and you get incomplete bonds. It has enough affinity for moisture that it will pull it out of the air to complete the matrix, but that takes time and can subject it to damage in the interim. A better substance is a sand mix (deck mud) or structolite for this application. Not sure what the lime (which makes it type S) will do in the long term...maybe nothing.