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.