Don't worry, they'll respond eventually.
The reason the submissions window is open less than six months is because they need the rest of the year to get through the massive slush pile. I sent a "tired" time travel effort early December, which came back after submissions closed (meaning I couldn't send another), giving a turnaround of about 12 weeks.
Sending something near the end of the submissions window means an even longer wait. I'm sure patience is mentioned somewhere in the submissions guidelines. You'll need it.