وَمُضِيُّ الْمُدَّةِ إِنْ لَمْ يَخَفْ ذَهَابَ رِجْلِهِ مِنَ الْبَرْدِ
Normally the wiping period ends at 24 or 72 hours. The text adds an exceptional case: if removing the khuffs and washing would create a genuine fear of loss or serious damage to the foot from severe cold, the normal expiry ruling is suspended until safety returns.