The working time is 8 hours. If you arrive at the company 10 minutes in advance, it will take Xiao Zhang 40 minutes to travel to and from the company, and the one-way trip will take 20 minutes.
When he arrives at the company, he still has 10 minutes to go to work, and the working time is 15, so his time to arrive at the company is 14:50.
It takes him 20 minutes to get from home to work, so the actual time for him to leave home is 14:30, and his clock shows 12: 10, so the clock stopped for 2 hours and 20 minutes.