I've had 3 encounters with the Jekyll and Hyde random event over the past week or so, all 3 of which I have been within 10 or so squares of a bank. This most recent one I ran to the bank and had a clean herb within 7-8 seconds, if not less, and the other times were similar but the event disappears. I've seen other random events stick around for double that, if not longer, such as evil bob or the mysterious old man.
If accessing the bank is what triggers the shortened delay or is a trigger condition for the end stage dialogue where they say "maybe later" stick around for two more seconds, and then depart, please remove that condition as they are still around but attempting to interact with the random event just prompts a dialogue box of "bye" and things like that. The event is still there, it should be usable.
Random events used to serve more purpose back in the day to ensure you were paying attention/not botting, but are now fun ways to obtain collectables, xp lamps, etc. give players more opportunity to engage with the random event, especially if it's conditional such as needing an herb to benefit from it.