The grocery store receives its delivery each morning at a time that varies uniformly between 5 AM and 7 AM. This is a 7 - 5 = 2 hour period in which the delivery is made with the same probability.
2 hours is equal to 120 minutes which is equal to 12 intervals of 10 minutes each. The probability that the delivery is made in any particular 10 minute interval is 1/12
If delivery is within 10 minutes of the expected time on any day there is a 20 minute interval; 10 minutes before the expected time and 10 minutes after the expected time in which the delivery is made. The probability of this happening is 2*(1/12) = 1/6
There is a probability of 1/6 that the delivery is made within 10 minutes of the expected time.