Pet fish! Please help!

So my husband and I got an aquarium yesterday and we got some red sword fins and a few others. The red sword fins mated and now we have little babies swimming around. I read that they can eat their babies if we don't keep them separate. My husband won't be home with a separate tank until 9pm tonight so I put the babies in a ziploc bag and set it inside the tank to keep the water temp the same. How long can they be in the bag before they die?