You may find
WWOOFing suits you; most hosts would want you for at least a week, but places like Lower Shaw Farm in Swindon do WWOOFing weekends.
Generally, the odd day or weekend is frankly something of a drain on a farmer / smallholder. If you can find somewhere near to you, then it's a better arrangement, as over a number of days / weekends you will learn enough to be genuinely helpful. If you have to travel far, it is harder to get the balance right such that both you and the farmer / smallholder gain.
Whereabouts are you?