Sevin, when you're defending a base and have sigils that you're trying to corrupt, if the enemy breaks through your defenses and puts most everyone in skill loss, they only have a limited amount of time to do something with those sigils before your side regroups. The enemy needs to get a thief in the sigil room to take the sigils and hand them off, one at a time, to other players to run to their own base. Then, if they can hold onto them for at least 15 minutes, that stops the corruption cycle for the other side. If the other side, however, manages to get the sigils back in place before 15 minutes from when they were removed from their base, the corruption cycle just continues as if there was no theft.
So, really, you don't want to shorten up that 20 minutes of skill loss by too much or it can turn the sigil guarding into a never-ending back-and-forth process that no one will ever want to do. Twenty minutes of skill loss gives you a slight chance of getting sigils back in time, but you really have to be organized and also hope that the other side runs into some kind of a snag or another.