I always do the freezes for 48hrs with the freezer temp setting as cold as it gets just to make sure its frozen real well.
I actually store my bark a certain way so the first freeze is out of the way when i use it.
What i do is powder 100g, fill a ziplock bag with powdered bark, add 25ml water at a time & mix until it's all wet & stuck together but not liquidy, then close the bag, zip another bag around that one & another one around that one & freeze.
If you have a large supply of bark you can do multiple bags & have them ready to start extracting at any time