I would always run Star San through even brand new beer lines. I often clean my lines, between kegs, and leave them filled with Star San solution until I put a new keg onto them. That can be anywhere from a few minutes to a few days (or more). IF the lines are closed at both ends (QD on keg end, and faucet on the other), you can leave them filled with Star San for an extended time. If they are left open, then I would run clean water (at least) through them and then Star San before putting them onto a keg.
Hopping Tango Brewery
跟猴子比丟屎 ・ Gun HOE-tze bee DIO-se
On Tap: Caramel Ale, Mocha Porter II, MO SMaSH IPA
Waiting/Carbonating: 12.5% Wee Honey II, 8.9% Old Ale, English Brown Ale, Lickah ESB, Mocha Porter II
K2: Epic mead
On Deck: Caramel Ale
Mead [bottled]:Oaked Wildflower Traditional, Mocha Madness, Blackberry Melomel, maple wine