The unit in 'period' is ns, which is default of WCT. With a tick being 0.5 us (e.g. MicroBooNE), a period=2000 ns would be a rebin 4. The current file is corresponding to a charge error calculation for a 2000 ns bin (rebin-4 for 0.5 us tick).
Note: it is possible that this rebin choie is different from the number of period, but it is strongly suggested that they are kept the same.