The Scott's are right. There are no hours requirements. I prefer to think of it as a "members trail" but it is certainly OK to bring non-member friends out to ride with you. As Scott Ellis said, I would like to see it get used a little more to keep it broke in.
Just remember, it is on private land and there is no parking other than along the road. So far the neighbors have been very receptive and I have not had any complaints, I hope to keep it that way. Most people I talk to in the madison area seem to have heard about the trail so I'm not sure how secrect it is anymore. But I'm still asking that directions not be posted on the internet.