I cosign with a week. I also like to enjoy the fresh from the salon look for a little while.
But I've gone as soon as one day after, and nothing has ever happened to my hair. Just make sure that your hair is really well neutralized and washed after the relaxer, and rinse your hair with water before going into the pool. If you smell relaxer when you rinse or if your scalp starts feeling weird, then I wouldn't suggest getting into the pool. If you smell nothing and your scalp feels fine, then go for it.