At least 6 minutes imo would be nothing more than a minor annoyance by the middle of the race.Or what Jumbo did this year at the Vuelta. If you're VLAB, how many minutes do you let Almeida take in a breakaway before you start burning doms chasing him?
Of course we've also seen the problem with this strategy --- you might be forced to back the rider you don't have that much confidence in.