When I was expressing when my two little ones where is hospital they told me that I could add the milk from one 24 hr period into one bottle.
I had the bottle in the fridge and when I finished expressing (into separate bottle) I would put it in the fridge and when it was at about the same temperature as the other bottle then add it to it. You shouldn't add warm milk (body temp) to cold milk.
Then at the end of the 24 hr period you can then freeze it for latter use.
Thawed milk will last 24 hours in the fridge and 4 hrs at room temp, so maybe take it out the night before and let it defrost overnight in the fridge to use the next day.