Frustratingly ... no
T2 allows you to change the hour only (which is expected) and in T2 mode, pressing LIGHT and SET toggles the chime on and off.
In T1 time set mode, I've pressed multiple combinations of buttons when hours are flashing, and tried to take it past 24 to see if it kicks into 12-hour mode after that, but nothing doing.
When in T1 'normal' i.e. not time setting, mode the SET button switches to toggle the chronograph, SELECT button shows the alarm (also in 24-hour time) and MODE button shows the date.
If I hadn't seen the PM symbol in the Elgin photo I'd have thought the Arctos was permanently a 24-hour clock!