The most simple answer to that question is this...When the wildlife decide its time to come in and water or wallow! Now try and decide when that is. Every animal and location is different. Use a trail cam and try to patern if you can. A friend had a 400" plus bull that would only water in the middle of the night. Every 9th day he would come in at 1:30 in the afternoon for some reason. He sat and waited on that 9th day and sure enough, the bull came in!