Possible Clues:

• Time of year when business is slack
• Winter at the Jersey Shore, say
• On land presumably lad's quiet time
• Time of year when usual activity or business is slack
• In less busy time, switch positions, swallowing lots of water
• Quiet time of year
• When business is slow
• Marine's leg getting strong in slow time
• Summer at a ski resort, e.g.
• Not much work here now, so away on your travels, my sailor-boy