They waited 18 hours to tell the townsfolk?

Just watched it again for the first time in 20 years, and I'm confused here.

So okay, they're at the bar having a few drinks the night before the volcanologists are set to leave (Harry/Pierce says he's leaving at 6am).
Harry and Mayor go back to her house to send the babysitter home. No one mentions the time, so let's say it's maybe midnight. Then Mayor sees the brown water, so she and Harry go check out the town's water supply, which sets off his "Oh Shit" signal.

So Harry immediately called Paul (his boss), waking him up from his sleep at the hotel, to tell him this urgent news.
Then Paul, Harry, and the rest of the scientist crew are at their computer room seeing shit go nuts on the radars and stuff.
Then Paul looks at Harry and says something like, "Call the mayor, we need to set up a meeting."

They didn't mention the time there, either, but I doubt they went to sleep after noticing the brown water. So you'd think pretty early in the morning, right?

But they don't schedule the town meeting until 6pm.

They put out the alert on the news, and the cop car was driving around town using the P.A. system to tell people about the meeting at the school at 6pm, but why the fuck did they make it that far out, when it's clearly an imminent threat?

They could've started getting the word out as early as possible (even 5am, who cares) and made the meeting for 12 noon, giving them a hell of a lot more time to evacuate everyone.

Did that seem weird to anyone else, or did I miss something?

(Of course, if they'd had the meeting earlier, and everyone got out and was fine, it wouldn't have been as entertaining for us, but that's besides the point.)