It depends on the host and the season. In winter there is often less things to do, because the animals are in the barn and the days are shorter.
The WWOOFing Charter stipulates that WWOOFers agree to voluntarily help their host for 4-5 hours a day, 5 days a week (approximately 25 hours a week).
However, some WWOOFers may wish to accompany their host throughout the day. This is permissible, provided that the intention is sincere and not suggested by the host. It is important to discuss this topic with your host before your arrival.