It is a logical consequence. If you have occasional intermittent active run spikes you need enough calibration time to be sure that whatever caused them has had time to appear in cal too - if it is the same for active and cal.
By that standard, we should reject the top quark and other rare events from high energy particle physics. They don't do blanks. If they spend 6 months colliding particles, after they find a few collisions producing what they are looking for, they do not spend another 6 months finding nothing before declaring success. The entire run is considered active. We should also reject all observations of super-novas, because after astronomers find one, they do not spend years not finding one, as a blank. (Astronomers don't actually look for them at all; the moment one appears is the active run, and there is nothing like a blank run. But the fact that they seldom appear is not taken as evidence they do not exist, or that they are are instrument errors, which is what your standard would lead us to conclude.)
A calibration should cover all likely events, and all variations in power levels or ambient changes. It should be statistically valid proof that the instrument is working. If you demand that a calibration last as long as the active run, that would lead you to reject nearly all cold fusion results, and most results in other experiments as well. People seldom do as many blank tests as active ones. They seldom devote as much time to blanks as to active experiments. Although, I would point out, Will et al. actually did more blanks, over a longer time, than their active tritium experiments, if you count their tests of unused samples. They got 4 out of 4 of the active cells, 0 out 4 of the control, and 0 out of 150 unused samples:
Since you reject Will et al. along with all others cold fusion results, you don't actually believe your own standard here. You made it up on the spur of the moment as an excuse to reject Zhang. You would make up some other arbitrary standard to reject Will.