If I understand correctly, once player A makes a draw offer, the opponent player B retains the right to accept the draw offer as long as player B does not rejected it verbally, or touch a piece with the intention of moving or capturing it. So technically player B may spend as much time as he has left on the clock, say 60 minutes, before accepting the draw offer and once the draw offer is made, player A is not allowed to withdraw it.
So what is the longest record of waiting time before a draw offer is accepted?