OG and Ferment time

Just made a fairly big beer last night and mistakenly added yeast before I took the OG reading, is that going to be an accurate reading? I put it on top a rather large yeast cake.
Beersmith estimated OG at 1.073, my reading was 1.069.
The other thing is with a beer that has a potential of 7+ abv, how much longer do I figure for fermentation time? Still just 1 week in the primary, then leave it in the secondary til it quits fermenting (FG levels off)?

The yeast in the wort won't throw off the OG reading, so you were probably accurate.

I'd leave it in primary until it's done fermenting, and then about 3-4 more days. It might be about 10 days or so, but it could be longer. You want to get to FG before even thinking about transferring it, and I like to leave it on the yeast cake about 3 days after that. Even after fermentation is over, the yeast are still working. They "clean up" after themselves, even digesting their own waste products (like diacetyl). A bigger beer may produce more off-flavors at first, so I'd give it a bit more time.

I know there's a sticky on this somewhere, but i guess the nutshell on when fermentation is complete is to check the gravity after the bubbling has stopped or at 10 days?

10 days works well for me-i have an oatmeal stout that has been in the primary for a week today, and all the action stopped about 3 days ago. i'm still going to leave it in the primary till monday or tuesday though-my OG was .070

I wait at least 10 days regardless of what the airlock is doing. If you give it 10 days in primary before even thinking about messing with it, you'll be in good shape most of the time. Then check your gravity and move to secondary if you wish, or just leave it in primary for 2 more weeks before bottling/kegging.