Option 1 -> "As though" introduces hypothetical or imaginary situations, not actual reasons.
Option 2 -> "Because of" requires a noun phrase, not a clause with a subject and verb.
Option 3 -> "Since" introduces a causal reason and works perfectly with a clause to explain why they'd get tickets.
Option 4 -> "Until" indicates time limits and doesn't fit the logical relationship between the clauses.
Hence, Option 3: Since -> The sentence needs a conjunction that shows the causal relationship between waiting all night and the certainty of getting tickets. "Since" means "because" and correctly introduces the reason for the speaker's confidence. -> correct