it is still showing over 300k and i just emptyed it

Same here - had 100sP in the till, took that out, refreshed (and hard refreshed) other pages, and the widget was still showing 100sP.

However, I walked away from the computer, came back about 30 minutes later, and when I refreshed the page then, it showed the correct till balance. So, I'm guessing there's a built-in time delay for the widget updating, rather than it being a real-time amount?

I think most people realize it's cached, but it shouldn't be thirty freaking minutes. It was instant before and should be instant again. If it absolutely has to be cached, it should be maybe five minutes, not thirty.

Sorry that is just how it is!