[FlorayG]

if your husband is paid an hourly rate and the employer could not reasonably have expected him to be back at the yard by 6 then yes, he is owed at least the time back or payment - though possibly not at 'overtime rates'
If he could have been back easily by 6 if it weren't for the traffic then the boss could just say it was a one off and sorry, shan't say anything if you finish a bit early on Friday
Depends how good the boss is