Look, if an arrhythmia doesn't show up in the first 24 hours, it's not that much more likely to show up in the following 24 hours. Although it's probably happened, I've never seen a "48-hour" Holter detect an arrhythmia better than a 24-hour Holter and all it ever does is increase costs (and torment the Holter reader).
If a patient has infrequent symptoms, consider an 30-day event (loop) recorder instead.
There. I feel better now.