1-1:30pm CT is the Houston window for Platts' product assessments, when most of the volume in cracks and related fixed price futures are traded OTC. Related but not directly is the CME's own settlement period for WTI futures, the VWAP between 1:28-1:30pm CT. The WTI/Brent screen volume increases during the window as most of the market trades cracks to get into fixed price positions or vice versa to get into cracks - whichever is more liquid for the product in question.
You can see the same uptick during the Singapore and London windows in Brent, however both at 4-4:30pm local time.