Ah, wait, your “3 hours” just triggered my recollection that the SMP has an energy saving setting, to shutdown after 3 hours without use! Definitely try turning that off if you have it on. It is under Setup > Operation > 3 Hour…
I have it enabled on one of my twoSMPs, but it never causes any issues with my Samba server. However, it certainly might cause problems with other servers (and will slow down restart).
As for saving energy, the SMP takes <5 watts while on. I don’t worry about turning mine off. I can drive a couple of miles less per year or switch another incandescent to CFL/LED and save more than that. I generally want my SMPs to start instantly and not have to reboot.
Being a server generally means running 24/7. Having clients running without the server being on can cause problems for many protocols. You might want to post a separate thread about best methods people have found for saving energy with SMPs. MIght require plugging drives into the SMP itself.