This beer is a way to make a sour beer while reducing contact with your equipment somewhat. Pitch the US-05 into primary, and then let it ferment out. Then, rack to secondary and add the lambic yeast. The wild yeast will pick up where the ale yeast left off, chewing some of the longer starch chains up and turning the beer sour, but not as sour as a straight lambic. It's more of a "Tart Blonde" than a sour one.
Once in secondary, feel free to let it sit for 6 months or longer. The longer it ages, the more tart it will become (to a point).
Also, a good variation on this is to add 5 pounds of fruit to secondary when you add the lambic yeast and it will really sour and also make some extraordinary sour beer. I prefer tart cherries if you can get them.
After about 6 months, I prime with some corn sugar and bottle it, and then it will continue to mature in the bottle for some time.