It was suggested that the timing of that moment to take a break would be a bit weird. 40 mins in and precisely between ATC. Doesn't make a lot of sense but then what does...?
Makes perfect sense as a theory to me. Overnight flight, a few cups of coffee before departure and probably over an hour since having a chance to use the can as the time pre-departure would have been tied up in preflight activities. Plane is at TOC on a routine flight, LNAV, VNAV engaged, benign weather, a routine handoff upcoming. Getting up to use the lav at this point in the flight doesn't strike me at all as odd or implausible.