I always start at market value + 0 Token because I don't know about the seller's team quality.
I don't think that is insult if I start with 0T offer, if you aren't willing to sell that player, just reject my offer.
I think there's no reason to hold 24h, because through that holding time, your player cannot train and gain anything, waste about 48% condition if he's at 99% condition when offer's coming.
BTW, I've never re-offered to a player that I had been rejected.