Logic calculation question

i keep finding the answer as 10 minutes, can someone double-check the answer? the answer key says B.

The small van driver’s shift - 1hr 10 mins. If the small driver gets back as LATE as he possibly can, then each shift from 1 pm will start at: 11.50, 10.40, 9.30, 8.20 and 7.10 The depot doesn’t open until 7.30, so the latest he can start to get the max deliveries is 8.20. which is 20 minutes after the large van driver starts loading. So the answer is B :))