Possible Clues:

• What some do while the sun shines?
• Seize the opportunity, sunshinewise
• Seize an opportunity
• Take advantage of the situation
• Be opportunistic, metaphorically
• '. . . . . . . while the sun shines'
• Spooner's swimmer might seize the chance
• Do it while you can, when the sun shines
• ''.... ... while the sun shines''
• ''. . . . . . . while the sun shines''