Save yourself time; understand engineering constraints early.
Don’t go through the heartache of falling in love with a design that’s out of the question because you didn’t understand the technical or time constraints early enough.
(And even if it is a design that’s worth going to bat for, your case is going to be much stronger if you do understand the constraints.)
The worst thing that can happen is that you spend your time perfecting a design that has no chance of working out. Good designers are scarce enough as is, and there are enough big problems that we don’t need that kind of inefficiency.
