While I was sleeping, the children were playing in the garden.
Here we have two situations of some duration going on at the same time.You can. I wasted some precious time yesterday. I was looking for John for three hours when I could have been working. I didn't realise he was sailing with his brother.I'm not sure if you can use past progressive + for + time... "I was looking for him for 3 hours"
Retired English Teacher