Stir-frying involves frying very hot and fast, with stirring all the time to make sure the food doesn't burn. You want the heat up as far as it will go, and with chicken pieces of that size I think they will be done in 3 minutes.
Now test - cut a piece open, and if it's white all the way through, it's done. Any longer and it'll be tough. You can't rely on any set times - be a real cook, look for yourself to see if it's done. It depends so much on how big the pieces are.
Then yes, remove the chicken, stir-fry the veggies until they're soft or how you like them (probably about 5 minutes), chicken back in, add sauce and let it all heat through.
I have a recipe for chicken chow mein which says exactly this - of course it has noodles as well, and if you want those, boil them in another pan following the instructions, drain the water off and mix those in at the end.