Yay! Congrats! You can remove the chicks from their mother at any time. I have hatched out my own (no mother present) and bought day-olds. So they will be fine, as long as they have a warm place with some food and water easily accessible. As for how long will she mother them, that depends on the breed, I think. My Silkie hens ditched their chicks as soon as they hatched. The Silkie roosters kept them warm at night by covering them with their wings and sitting on them.
Just make sure that if you separate them, it's warm enough! We've been having 36 degree nights, which I doubt would be be good for a week old chick.