«وَإِذَا نَزَلْنَا مَنْزِلًا أَوْ وَرَدْنَا مَنْهَلًا»
Whenever we stopped at a campsite or reached a watering place.
Idhā is a temporal conditional that does not itself make the following verbs jussive. The perfect verbs nazalnā and waradnā, coordinated by aw, describe alternative recurrent stops.
The contrast between a campsite and a watering place helps map the travellers’ routine. In English, “whenever” reflects the habitual context better than reading every past verb as a single isolated event.