None of these options give me warm and fuzzy feelings here.
Sleep: Great idea until you die horribly
Wake Selina: What is the point of no one being rested? At that point you might as well explore.
Tough it out: Shinji falls asleep, or spends a super long time going mad. Plus I think this pushes Shinji to the breaking point, in that he barely has sleep, hasn't eat much and keeps casting magic.
Right we need to buy a plain old not super expensive old-timey pocket watch. Add that to our list of survival stuff that we need.
Rolling a die here for what option Shinji picks here...you darn noble fool.
[X] Tough it out till Selina's time to...wait a minute, there was no light from outside, and he had no timepiece. Until she woke, then.