The 'time' view of the 'Reputation' view has, it turns out, some properties you wouldn't expect.
Reputation changes that occurred more than two days prior are displayed with a time stamp that gives date, hour and minute.
However, for changes of reputation that occurred two days prior only the day is given in the direct view. It turns out that in that view more granular time is available as follows; when you hover over that date a tooltip appears that gives the time down to the second. (This was pointed out by contributor 'Amit', in a comment to the answer by contributor 'rob'.)
As I accessed the 'time' view on the 25th of May the timeline was overcrowded with the recent serial voting, such that older entries (which display with date/hour/minute in direct view) were pushed out of view.
(Access to older reputation changes is provided in the form of folded entries. If I would have unfolded one of them I would have seen the date/hour/minute time stamps there.)
So:
As I didn't know about the after-two-days change, and didn't know about the tool-tip-on-hover: it looked as if stackexchange never displays hour and minute information, and that is why I posted this question here in physics meta.
The past couple of hours some upvotes have trickled in, bringing the difference into direct view.
The less-than-24-hours-prior reputation changes are given in the form '$x$ hours' ago.
For the time frame between 24 and 48 hours prior that will change to the date (with tooltip-on-hover).
After that the view will change to the date/hour/minute form.