Possible Clues:

• Twenty four hour - hour
• Twelve of ours, by the sound of it
• Non-stop golf - source of trouble he has with grandfather, for example
• Ours by the dozen, by the sound of it
• 24-7
• As some golfers play, all day and all night
• That's twelve of ours, by the sound of it
• What some golfers play all day long
• Twenty-four-hour (operation)
• Twelve o'clock?