Modern strings do not need much tensioning. I have watched a soloist experience a broken string in mid concert and replace it in not much more time than it takes to cough with embarrassment. A cautionary note when buying new,unwound strings. Don't bring along your old tube with some spares still inside it. It looks suspicious when you go to the pay desk. You feel like bank robber, even if nobody accuses you. If you are buying a complete set, they probably come in a new tube anyway.