If you hang around social media groups or chat boards for writers & artists, you’d have run into mentions of the best and worst times to submit work for consideration, and the questioning of whether there is such a thing.
I’ve read that “the holidays,” any of them, are not a good time. I’ve heard that international book fairs (unless you or your agent are part of the fair) are not a good time. I’ve heard that while neither snow nor rain nor heat nor gloom of night will stop the postal service, these are not good times for agents, editors and art directors.
If you believe all that, you’d have a dim view of the publishing world. It would appear these folks never seem to work.
In my personal experience, there are no “bad times” to offer your creative output to the world. But my personal experience is too limited, so I turned to a few much-published friends, and they confirmed that my experience is just like theirs. Acceptances come during the winter holidays and in the middle of summer heat.
So if you are using the fact that it’s summer as an excuse, (because we know that August is around the corner and, well, New York City shuts down in August, doesn’t it)—Please don’t.
The best time is when the work is ready.