I believe 12 hours
To the best of my knowledge, there are no laws governing this aspect of employement. In other words, your employer could have you work 24 hours a day, 7 days a week, as long as they pay you overtime...
It is 840 miles according to Google Maps.
6 hours
A full tidal cycle occupies nearly 13 hours. Approximately 6 hours and 13 minutes each time, adding up to 12 hours and 26 minutes total.