Hi Violet,
Just to further up on Rick's posting, we got ours after our structural appointments. So depending on how recently you bought, you may have to wait a while. Here are some milestones we have encountered so far, that you can look forward to:
#1 (Obviously the first was the purchase)
#2 Going out to the site and seeing the land cleared for construction a month or so after purchase - yours must be cleared now too.
#3 Exterior colour (aka brick) appointment
#4 First and second (and third etc. if necessary) structural appointments.
#5 Interior colour appointments
By then they should be almost ready to dig your lot and get started on building the house. From what I gather, most people have their Mattamy U. dates sometime close to this beginning of the construction (either a couple weeks before or after they begin building).
By the way, I lost a bet this weekend.

They haven't started to dig our lot yet. The bet was that they would by June 12. Our next door neighbours have basement walls and we don't even have a hole yet! Argh!!! I hate losing. It's not the money (it was only $5), but rather the fact that I have to go back to a friend who will no doubt be very smug about her intuition. (grumble, grumble......)