You can pick up a SC via CCS or Crew Companion. I have run into glitches in the past with Crew Companion that have caused me to miss picking up SCs that I would have wanted. If you don't pick one up yourself, CS can and will call to assign one and they do it according to your Silo.

When SCs happen to become visible in CCS/CC varies greatly along with the number available. Usually, they first pop open for the next day at the 1100 APU window... sometimes they don't come open until around 1pm.... and sometimes I barely see any. If I intend to play SC roulette, I do so with the intent of showing up as late as possible my first day on reserve or getting released as early as possible on my last. That is why it is important to put in SC pickup requests in CC and to back them up by checking CCS at 1100/1300ish.

Once you have picked up say a 2000 Tuesday SC via CCS at the 1100 APU on a 'last-day-off' Monday... you are not going to be called until 2000 Tuesday at the earliest (unless maybe they release you from SC to assign you a trip in 12 hrs). I got hosed badly the other day after picking up an 0200 SC and with no open trips visible at 2300 bedtime... they called at exactly 0200 for an 0430 mx ferry show time. *&^%$#$@%*!!!!!

A SC officially lasts 14 hours, but after 11.5 hrs you are effectively unusable even for a DH (unless you agree to accept extra pay to be at the airport in less than 2.5). It is not unusual to get released a couple hours early from a SC that will go unused... and be assigned a trip with a showtime in 12 hours. You still get credit from the unused SC though.