What is the unit for measures on the colorbar in Hilbert spectrum?

When applying hht(imf,fs) we get Hilbert spectrum showing a colorbar on the right. I am wonderin to know what the unit for those values/measures is on the color bar and how can we obtain/calculate them?

Meanwhile, how can we customize the actual time on the x-axis, if offset is other than 0 (f.exp. 25-30s)?

Thanks in advance,