Possible Clues:

• Twenty-four hours of sea duty, doing shifts
• When you vote, usually
• New duet, say, that lasts twenty-four hours?
• Eager beginner in a study, working for one day a week
• Irregularly, stayed outside university for part of the week
• After travelling, you finally stayed for 24 hours
• What the 'Mardi' of Mardi Gras means
• Sea duty arranged — twenty-four hours
• --- Weld, actress
• Mardi Gras time