Possible Clues:

• Sea duty organised for 24-hour period
• see 1 Across
• Calendar column ... or a punny hint to the circled squares
• There's one in every week
• 14 Across day
• Ruby ---, Rolling Stones hit
• Sea duty (anag.)
• Unsteady rocking not new — it's a regular occurrence
• Used to swim in river early in the week
• Third in a sequence