وَكَذَٰلِكَ بَعَثْنَٰهُمْ لِيَتَسَآءَلُوا۟ بَيْنَهُمْ قَالَ قَآئِلٌ مِّنْهُمْ كَمْ لَبِثْتُمْ قَالُوا۟ لَبِثْنَا يَوْمًا أَوْ بَعْضَ يَوْمٍ … فَٱبْعَثُوٓا۟ أَحَدَكُم بِوَرِقِكُمْ هَٰذِهِۦ إِلَى ٱلْمَدِينَةِ فَلْيَنظُرْ أَيُّهَآ أَزْكَىٰ طَعَامًا فَلْيَأْتِكُم بِرِزْقٍ مِّنْهُ وَلْيَتَلَطَّفْ
"And thus We awakened them, so that they might question one another. One of them said: 'How long have you stayed?' They said: 'A day, or part of a day'… 'Send one of you to the city with this silver coin of yours; let him look for which food is purest and bring you a provision of it. And let him be very careful.'"
لَبِثْنَا يَوْمًا أَوْ بَعْضَ يَوْمٍ — the same measure was treated in al-Muʾminūn at 23/113 (labithnā yawman aw baʿḍa yawm) and in al-Aḥqāf at 46/35 (sāʿatan min nahār). In all three places a long stretch of time is supposed short.
And the difference here must be recorded: the others are said in the hereafter; this is said in this world — and those who say it are wrong for good reason, because they have just woken. That is, the sūra shows the misjudging of a length of time not as a defect but as the limit of the human instrument of measure. I record this as my own reading.
ل-ط-ف root: fineness, gentleness; to act quietly and with care. The word was treated in Luqmān at 31/16 (laṭīf).
I record this as an observation: the most detailed command in the story comes on the smallest matter — being careful while making a purchase. And the reason is in the next sentence: wa lā yushʿiranna bikum aḥadā — let him make no one aware of you.