Michael -- to tell you the truth, I don't know when camp does officially begin, but as a result of purchasing a 10 game package, I got on an email list for upcoming events, etc and I just got the following which is an extract of the email:
Save the Date - Open Scrimmage
The Spurs will host an Open Scrimmage featuring the full team roster at the AT&T Center on Sunday, October 6. All Season Ticket Members are invited so mark your calendars. We will alert you via email as more details develop.
You can't be late until you show up.