4 hours and 48 minutes.
However, that would break union rules, and he would be due several T breaks of 10 minutes, plus a trip to the toilet. This would add a further 24 minutes to the job. Unfortunately while at the toilet he tripped and hit his head on the floor and had to be taken to hospital. On arrival in casualty, a more urgent case arrives, knocking back his slot for a further 40 minutes. Given the all clear he returns to the site to find someone has nicked all the bricks. He mut now wait until Monday to get more delivered. In answer to your question - it all depends on what other factors take place during the job. So the question is unrealistic and you would be better to highlight this in a 2,000 word essay.