There is not really a way to cut these enough to let in a whole bunch of light that will also suit the trees. And if they keep doing well they will get much bigger in time than they are now, filling that part of the yard with yet more roots and shade.

Maybe you should instead think about having them taken out, before they get bigger and more costly to have removed.

Just to be clear what you are dealing with, there are planted silver maples with average crown spreads of 90' or more; heights above 100' are rather typical for the species.

Silver Maples roots make it very hard to grow a nice thick lawn anyway, in the long run, and the trees will keep getting bigger with more roots. And would you keep trying to trim the trees? It will be a struggle you will lose I think.

Maybe using the money on the lawn would be a better use... shade seed, fertilizer, aeration. And/ or remove one of the Maples.

I don't think it's as much a matter of timing as it is proper technique. I think the proper way to trim a silver maple tree is a lateral cut across the trunk about 6 inches above the ground. Afterwards, a large machine can be used to grind the stump into a nice hardwood mulch.

Get rid of them before they start dropping massive limbs onto whatever is unlucky enough to be below them.