“Daycare centers generally follow formula rules. Fighting this is often not possible. One of the many reasons to send smaller frequent bottles instead of larger less frequent ones is to avoid waste of leftovers. Many daycares dump milk after one hour, just like formula.
some daycares will put leftovers back in the fridge "so you can see how much" and let you take them home to deal with (ie repackage)-outside of day care (in home, nanny, etc) it's generally ok to leave warmed milk (or milk taken out of the fridge) at room temp for 4-6 hours to reoffer if bottle is not finished.
Also generally reasonable to put leftovers in the fridge to use the next feed/next day (since my kids are in daycare MWF only and we don't ever do bottles when I am home sometimes my leftovers go 48 hours and back to daycare, I have never had a problem with this, only fresh milk used for this, not frozen, if there's previously frozen milk leftover I let her drink on the way home if she wants)”