location? You do not mention what state you are in--nor what type of grass.
The label for Dimension says something like after the second mowing. But it also says something like with good rooting system and well established.
So mow again and sock it on.
Water it in after--just to get the pellets into the soil. No need for special water after that--just do what you need to do to keep it from getting brown.
I am doing some quick and dirty experiments to see if the Dimension label is right or perhaps a bit conservative. So far Dimension was applied to small flower pots growing new grass that is 2 inches tall--no harm to grass visible yet.
I am planning to try applying Dimension to new grass I planted today to see if it can be applied to very new grass, and yet be in time for crabgrass control. Waiting for new grass to be about 2 inches tall before I treat it.