How to use `timing.err` in plot.biwavelet ?

[vsimko]

Dear @mccreigh / @jmccreight,
Thanks for your contribution to biwavelet.

I tried to create some unit test for your new type parameter timing.err in R/plot.biwavelet.R but I realized that I actually don't know how to use it. Could you please explain how it works and provide some working examples?
Thanks,
v.