Setting default PSD duration for long signals

Currently, the default PSD duration is 32x the segment duration. However, I learned from https://arxiv.org/pdf/1907.06540.pdf that for longer duration signals there is an additional constrained that the maximum PSD duration be <= 1024s (see Sec 2B).

This should be an easy one to implement.

/cc @avi.vajpeyi and @colm.talbot