How often to restart my Directstream dac and PST transport?

This is the first I have learned of this method being an option to optimise the electronics PWT.

Does it need to be carried out on a independent device or when the DAC>CDT are used in conjunction   

I don’t think it matters. I restart my dac and transport from time to time with improvements in sound. I recommend the Jkrichards nickel core transformers and VOCM mod. The improvement is more than subtle.I may one day upgrade my Directstream dac modded for a Mk2 but for now I am getting good sound.

Powering on and off has the effect of helping capacitors to break-in.

I like to do this when I'm going away for a few days.