Hi, my DS has worn glasses since he was 2 and was patched shortly after this.
4 year olds can be quite difficult to get to patch and the reward charts are great. He can tick a box when he has done the four hours, and a treat when he has filled x many boxes.
I would also try and patch first thing in the morning, you may be able to get a couple of hours done before you have to be anywhere iyswim.
When my DS was patching he was nursery and the staff were fab at making sure he kept it on.
It is difficult though, I empathised totally with DS because with his patch on he really couldn't see much at all, even with his glasses on. He would hide them everywhere, flush them down the toilet, peel just the tinniest part away and spy through the gap! Had to be quite strict in the end!
I was really upset about it, and I had worked as a dispensing optician/ manager for years, dispensing childrens glasses. It's true - it's totally different when it's your own!
Still, in the end it all worked out and although he will always need glasses, his vision is much improved because of the patching.
Good Luck.