Agreed. Stro or Giles could get hurt, their performance might fall off (see Happ's July last year), etc. Also the sooner a trade happens, the more control the receiving team gets. It won't mean much now, but two more Stroman starts if he's traded before tonight could mean something to the team acquiring him.
There is no right answer, but risk by holding too long is definitely big. Teams are not stupid anymore. There are no AA 2013-15 GM's anymore. What teams are offering now is probably what they'll offer a week from now, at least the bigger names.