Growing up on a farm, this made a lot of sense. You had to work on sunny days. Now that I am no longer on a farm, this means something a little different to me.
It means work while you can. Work while you have the health and ability. While conditions are good, make the most of them.
Because on actual sunny days, I like to watch my kids play, stroll with my wife, go for a run, or have a siesta under a shady tree. Sometimes even drink a cold beverage.
Words and phrases can mean different things to different people or even the same people but in different circumstances.
Do the work, or go and play, while you can.