That kind of depends on the cloudy conditions which (in my mind) would mean some overdevelopment instead of underdevelopment. As your film/developer combo (including your way of metering etc...) gives you a "max of 200EI", I would at least go for a normal time, else the negatives will be lacking too much contrast.
But you actually contradicts yourself in that you say that you wanted to use an EI of 500 while you later on states that you have a"a max of 200 EI". That is, you're not 2 full stops off, but just 2/3 of a stop!
You don't mention if you use e.g. VC papers or whatever, but if you can get grade 3 or maybe even 4 with your paper you should be fine. This because slightly overexposed negatives are easier to print than underexposed. You just need to expose the paper a bit longer. A thin negative which only gives just about an acceptable print on grade 5 is quite boring, while you're at the other end.
Without any real hints, you seem to use only one developer (which is a good thing), but if you have any other developer which is less "active", that could be an idea, but again with normal development you will have slightly (but not heavily) dense negatives which are somewhat low in contrast, thats all. If you overdevelop you will get quite dense negatives with large grain. If you don't print too large you just will have to wait some seconds more while exposing the prints, which again is all that will happen.
//Björn