Yes you can freeze milk in Ziploc bags.
However it's best to use freezer bags for freezing the milk because the freezer bags are tougher than regular Ziploc bags are.
That means they will not tear as easily as the regular Ziploc bags would.
Also the way I freeze milk is to put the milk into ice cube trays and then take out the individual ice cubes and place them in freezer bags.
Then I have a lot of frozen milk.
And when I need a few milk ice cubes I take them out and use them.
But you can freeze the milk in Ziploc bags by just pouring some milk into the bag and sealing and freezing it.
Once frozen milk is defrosted the frozen mil will last for up to 7 days after you defrost.
Make sure you store any thawed milk in the refrigerator if not consuming it within 30 minutes to an hour or it can go bad.
Freezing milk is a good way to make the milk last longer than just refrigerating it however just be aware that when you freeze milk the taste of the milk can and will change the longer you freeze it.
Frozen milk will last for up to a year and sometimes longer but the longer you leave the milk in the freezer the less tasty it becomes.
But it will remain safe to drink.
If you freeze milk and then defrost it make sure to drink or use up any thawed milk within 7 days of thawing or defrosting it.