That should be fine, and is probably what most people do as these things tend to be sent out all at one time. Same with GRE scores, as really no one applies during the summer, but it's a normal time for scores to be sent. I know I didn't finish some of my statements and applications until quite near the deadline. You don't want to cut it that close with transcripts.
Keep in mind, though, that many schools will require these things to be sent electronically. This means that your unofficial transcripts will be sent at the same time as when you apply, though your recommendations will be submitted online separately by professors, etc.