the conditions of the dropped candy and the acuity of your vision govern the amount of prejudice of the rule. the time limit is only for show.
if you can wash it off, there are no rules, no time limit. (so long as you know when the candy was dropped, not for for candy you find sitting around
if you can't rinse it, any candy dropped that appears to have not picked anything else up is ok. the 5 second rule applies just for superstition and posterity here.
candy by it's nature is sticky, so it probably will find a cat hair, ball of lint, or chunk of something dark to stick to it, even if you catch it on the bounce.
therefore, if you can't get it clean, either take the loss, or be demure whilst spitting out the chunks.