Step 3:
While you wait, you might as well go ahead and mix up the sauce-
4 Tbs. white vinegar
2 Tbs. water
2 Tbs. ketchup
5 Tbs. sugar (yeah, I know)
1/2 tsp. salt
1 TEASPOON or so of corn starch. You can change this to adjust the consistency of the sauce, but I wouldn't recommend it unless you really know what you're doing since you won't be able to tell what the final product will look like until you heat it. The first time I made this I think I accidentally used a tablespoon, and when the sauce cooled off a bit it got kind of congealed and nasty.
Really, don't worry that it doesn't look anything like a decent sauce, I was somewhat suspicious the first time I tried it too. Don't worry if it has what looks like "chunks" of ketchup, that will be taken care of. Get all the cornstarch lumps out, though.
Around the time the meat is finished marinating, go ahead and set your stove on the highest heat, and maybe put your wok on there.