hi Senna,I give it for a whole week,once a month.Like other's,I find it easier to always do this for the first week of the month.
Dilute it 20mls in 1 litre of water.
If your hens are put off drinking their water,add 10 mls to water on day one,15 mls on day two and the 20 mls on day three.Mine don't bat an eyelid at having a week, where their water tastes different.