For hair to successfully be removed by waxing, the rule of thumb is that the growth needs to be about ¼”. If it’s shorter than that the wax may not be able to grasp on the hair to remove it. If you have noticeable stubble it doesn’t mean you necessarily have to wait to grow it to that length or resort to shaving. Here’s some advice for waxing at home, seeing the pros and application tips for using strip (soft) or stripless (hard) wax in: Waxing Short Length Hair.
But don’t think the longer the better. If it’s much longer than ¼” then you could risk other issues like missed hair, breakage and more pain. But of course this is much easier to tackle because all you have to do is trim it. Learn more about the issues from waxing hair that’s too long and how to correctly trim it down evenly without cutting some too short in: Tips for Waxing Long Hair.