I say zero days.
To me, “dibs if split” is just indicating interest. Since the guy didn’t offer to sell those chips separately, there is no offer to accept or to dib.
The dibs if split chips are almost invariably either the fracs or the highest denom (in other words the most valuable chips in the lot) so they’re likely going to be priced at a premium if sold separately. They might even be included in the lot as a loss leader. Maybe the seller wants to auction those off. Maybe he has a friend who wants them. Or maybe somebody has already shot him a PM and offered him stupid money for them. Who knows?