You can try that. But likely the tomatoes are already infected but won't show the damage for several days.

I've been doing just that. Some ripen OK before the blight spots get too big and some don't. Today I made roasted tomatoes to freeze, by cutting out the blight spots on the ripest ones and roasting with garlic and herbs. I salvaged at least a little of my harvest that way (though I would normally be getting tomatoes for another 6 weeks or so, and I may have 3 days left if I am lucky.)