1. Start both hourglasses at the same time. By the time 5 minutes pass and the 5-min hourglass is up, 3 minutes are left in the 8-min hourglass. (5 minutes)
2. The moment that happens, turn the 5-min hourglass upside down. Wait another 3 minutes for the 8-min hourglass to run out. By this point 3 minutes worth of sand will have collected at the bottom of the 5-min hourglass. (8 minutes)
3. Turn the 5-min hourglass back over again and wait for the last 3 minutes. (11 minutes)