Though I don't know any more details about the events that took place, there are several ways of speeding up the process. As 23kt gold is quite soft, it would b

Though I don't know any more details about the events that took place, there are several ways of speeding up the process. As 23kt gold is quite soft, it would be a quite straightforward process to finely divide it and thereby increase the reaction surface area. Additionally, you could (gently!) heat the solution, though at the cost of a more copious amount of nasty fumes.