As long as you're past the cure time you will be fine.
Pay close attention to the grout installation before you clean.
Get a spray bottle of water and mist the floor in several areas.
Then see what the grout looks like.
Is the color even?
I've seen / done several new construction T&G jobs where the grout was poorly installed.
Not visible under the dust and debris but voila, once it's cleaned the grout looks terrible.
And of course, it's your fault!
Set expectations up front.
Then light solution of GM at 1 scoop per gallon and 800-1200psi with a spinner is fine.
Sell them on sealing...