I have a pen very similar to yours. I also use hay. I do not put food or water in there at night unless it's extremely hot and then it's only water.
I clean it out every single morning right after letting them out for the day. I take my garden fork and put it gently under the poo patties and lift them out of the pen and into the yard. I have 2 pens and it only takes me about 10 minutes to do both. When the hay gets thin on my feet I replenish it.
I have found that if I do not clean it early every morning I will get a ridiculous amount of flies. I only let it go one time since it's gotten hot and will not do that again. I think I cleaned it just after noon and it was crazy with files. I can't imagine letting it go for a week!