Each errand is 15 minutes. But the transitions between them (driving, parking, getting distracted in the store, checking your phone in the car) add up to hours. Your brain estimated the errands but not the gaps. A backward plan from when you need to be home gives each stop a time box, including the transitions.
You budget 15 minutes for the post office, 20 for the pharmacy, 10 for the dry cleaner. That's 45 minutes. But you forgot the 10-minute drive between each, the 5 minutes finding parking, the 15 minutes you spent browsing at the pharmacy, and the phone call you took in the car. The errands took 45 minutes. The afternoon took three hours.
Ready Time works backward from when you need to be home. Each errand gets a block that includes travel, the stop itself, and a buffer. When the notification says "head to next stop," you leave, even if you haven't browsed every aisle. The time box keeps each errand honest and the whole loop on schedule.