Anytime after three PM is a good time to watch the weather tomorrow.
The system that spawned multiple tornadoes in Oklahoma on Tuesday will be camped on the St Louis area by noon...we are in the bullseye tomorrow:
...3 PM to 9 PM Wednesday afternoon and evening will be the open window for very severe storms across the St. Louis area. Baseball-size hail, torrential rain, deadly lightning and the possibility of large, damaging long-track tornadoes are all significant threats in the Mid-Mississippi Valley into southern Illinois...
I'd keep Joplin in mind and watch the skies very, VERY closely tomorrow afternoon.