I didn't find the "Clock" option on my control panel. Just date and time, which didn't have any regional options.
I've heard of the DFO CP, but I haven't tried it yet. Thanks for the suggestion, I'll download it once DFO finished updating to Act V a second time.
And actually, I don't get the black box. (Though I did when DFO worked for those two days; I just left it alone and it'd enter full screen after a little bit.) The DFO updater launches, uploads any available patch files, then closes, and nothing else pops up after that; no warnings or anything and especially not DFO proper. I've checked Event Viewer if there were any error messages that didn't openly show, but so far I haven't found anything.