You're not 8 or 9 days from expecting AF. You're more like 1 or 2 days from expecting AF.
Your luteal phase should stay around the same length most cycles. I understand that your cycle is usually much longer than this, but you
ovulated 10 or so days
earlier than usual. That means AF will also come about 10 days
earlier than usual.
But in any case, there might not be any reason for a two-day dip like that. Just as long as it doesn't go below the coverline, you're okay for testing on the day AF is due. Which for you is tomorrow or the next day.