On the few occasions that I've been unfortunate enough to have a coughing fit during any kind of a performance, I have immediately left my seat and sought a quiet place until I can get my throat and lungs to calm down. Thirty seconds? Okay, but barely. Ten minutes? Sorry, no. Before the end of the first minute, one knows that it's either going away or it's not, and if it's the latter, one needs to vacate the premises out of consideration for the other patrons. (This applies whether the person was ill to begin with or simply the unfortunate victim of a tickle that just won't go away.)
This extends, by the way, to people who slowly and loudly unwrap cough candies for a period of time measurable in minutes. Do it quick or leave the room to do it. You aren't being subtle; only a deaf person could fail to hear the wrapper scrunching. (One of my pet peeves; the worst offender is a lady in my choir. I timed it one time when it was a case of either do that or scream in frustration. It took her ninety seconds to unwrap that cough candy. That's an eternity when the minister is trying to make an emphatic point during a sermon. Egad.)