Question re: sunglasses and timing

[Tical]

For those of you who wear shades at the table, but only when you're in a hand (a la Raymer):

What's your habit of when you put them on? Every hand you decide to play, even if you're just limping into a family pot? Only when you call/raise a significant amount? As soon as you become a blind? Yeah I know its a dumb question but I'm just curious...thanks.