Somewhere on the listing it there is a "processing time" and the default is 3 days, as I remember (business or calendar? I don't know).
I think the maximum it can be pushed to is a week, but I may be mistaken.
Extenuating circumstances happen but are rare (illness, weather, personal emergencies, etc).
And a major personal crisis might well push responding to ebay messages to the bottom of the priority list.
But reminders every other day for about a week followed by a message to ebay is entirely appropriate.