Fa-lammā combines a narrative connective fa- with temporal lammā, “when ... then.” Ajaznā is a first-person plural perfect: “we crossed” or “passed beyond.”
Sāḥata al-ḥayy marks what they passed. Wa-ntaḥā and binā baṭnu khabt evoke a turning or moving toward a new place. Together the clauses supply a temporal and spatial setup for the action that follows.
Translation alone does not capture the full value of lammā. Its narrative-syntactic function builds anticipation: once the pair leave the settlement, the next event will occur in the newly described setting.