So, I decided to research these golden slime casino dates when a friend told me he found a correlation, here's what I found

The dates(starting 2018)

Jan 19th to 26th
Friday to Friday

March 2nd to 7th
Friday to Wednesday

April 6th to 8th
Saturday to Monday(Outlier)

May 4th to 11th
Friday to Friday

June 13th to 19th
Wednesday to Thursday

July 13th to 19th
Friday to Thursday

August 24th to Sept 2nd
Friday to Sunday

Oct 3rd to 10th
Wednesday to Wednesday

Okay. We have two outliers, but we're going to set them aside.
1. There was no casino in February.
2. April's casino started on a different date and was much shorter.

Other than that, there's two things to notice.

Casino always starts on a Wednesday or Friday

There's between 24-31 Days between Casino end dates and start dates

The reason for the variation in dates is because grey havens wants casinos to start on Wednesdays and Fridays. Causing the range.

What does this mean?

Casino is an entirely predictable event unless Grey Havens says otherwise. The last end date was October 10th. So in order to meet the criteria. The next Casino is either this Friday or next Wednesday. Pretty cool right? This also line's up with the end of Dark Harvest, so I'm guessing that it'll be tomorrow. However, if it doesn't start tomorrow it's definetly starting Wednesday.

This pattern does not apply if you go back into 2017 and 2016, Casino was entirely random back then. My data will remain true until Grey Havens decides to mix up the pattern, hopefully they don't.

So let's say this month's casino starts tomorrow, ends next Friday. Then the next Casino would be around December 5th or December 7th. Ending around December 14th, perfectly setting us up for Winterfest.