Cysts are not guaranteed to be killed without a 4-hour wait. I've read that the dose can be halved if the waiting time is doubled. So, you might want to consider treating water for the day the night before. Less chemical=better taste and less for your body to deal with.

Also, water that you use for cooking does not have to be treated first, as long as you are heating to a minumum of 180 F for common disease-inducing micro-organisms, hotter & longer for cysts.