I have a simple battery powered Hozelock timer which I use when we go away. Had it for years and it's been fine so far. Can't tell you the model without turning the shed inside out to find it. Sorry.
I attach it to the tap and then fit a Y connector and two hoses. One goes to the greenhouse and one to a sprinkler Which covers all my pots and troughs and baskets collected together for our period of absence.
I do test it for a couple of nights before leaving and always change the battery, just in case.