Dear To Wait or Not to Wait…
Submit when your project is ready. Some agents may have vacations planned for summer, but plenty don’t. And there’s simply no reason to try to “crystal ball” their schedules—if they’re fast responders, they’ll probably respond in their usual manner during summer, and if they’re slow responders, why not get into the queue now? I’ve asked this question of agents in the past and did so again after getting your question, and “Don’t wait just because it’s summer” is their common refrain.