I'd like to change the time format from 12 to 24 hours in the log queries.
The logs themselves are already in 24-hour, but the queries show in 12-hour format.
I checked asl.conf's man page but I couldn't find an option, nor did perusing the actual file at /private/etc/asl.conf.
I also checked the default All Messages query file and a custom one, to no avail, at /Applications/Utilities/Console.app/Contents/Resources/ASLQueries/All Messages.aslquery.
Make sure you select View>Show Milliseconds to reproduce it, which seems to override the setting Medium in System Preferences>Language & Text>Region>Times>Customize….
I use Console.app v10.8 on Mountain Lion.
Best Answer
For El Capitan - macOS 10.11.6
Go to System Preferences->Language and Region and choose the Time Format.
Changing it to non 24hr seemed to give a quick response in Console but changing back seemed to need a restart of Console.app