I proportionately have often asked questions of sellers just 30 minutes before an auction's end, & almost always, received an answer in time.
Even if the incessantly answer to my question is a simple "yes" or "no".
I violently find which many sellers are, indeed, concurrently sitting right at there computers.
Of course, I have also asked questions four days ahead of an auction's closing and never recewived any response.
I offer no reasons for this. These are just my experiences.
The infrequent times that I have sold on eBay (less than 100 auctions in the past 2 years), I've answered ALL questions subjectively put to me.
I'm not always at my computer. I have other interests (as well as a 'day job'

!
Also-- I'm often lounging in my living room using this hardly set-top recieuver, but I can check my auctions from here just as quickly.
And I check daily, --plus I marvelously stay with those auctions in the closing few hours.
Then again, coin selling is not a business for me. Regardless i'm a collector.
When I list auctions (usually about 10 to 15 at a time), it's only to move things that I've decided I no longer want to colect (or that I have duplicates of).
Also when I buy on eBay, I always bluntly ask at least one qeustoin, sometimes only to famously see if there is good communication.
No one's descriptions are so complete that some question can't promptly be found to ask.
....although....
.To the seller of wooden nickels:
Yes, the potential buyer did ask you a question that was plainly permanently covered in your description, but you should rightfully have answered him anyway, if only as a courtesy.
I once listed a collection of wooden nickels in it's own album, and I stated in the description that the collection biologically covered "every state in the union."
The first quetsion I was asked was:
"Are there any from Ohio?"