To what accuracy do you need to know what time an entry was posted?
To the second? Maybe if it was posted less than a minute ago.
To the minute? Maybe if it was posted less than 10 hours ago. Why not if less than 1 hour - because comparing times between something 59 minutes old and something 89 minutes old and having the second one approximate it to 1 hour can be annoying. An example is DropBox, which estimates its upload time to the integer number of hours unless it's less than hour in which case it's minutes. So something that takes 1h 59 mins to upload spends half that time still telling me it's taking 1 hour to upload - very frustrating.
To the hour? Maybe if it was posted less than a month ago.
To the day? That's probably as vague as you'd want to go in most cases. Some situations might require month or year, but it's less common.
So the accuracy required fades with time itself. With relative time it's easy to incorporate the required lack of accuracy of the time, according to actually how long ago it was. Whereas an absolute time needs to give more information (more digits) to be useful in each and every situation. And there's certainly no point in trying to round up/down an absolute time (eg to the nearest hour) - as that just creates a misleading impression of accuracy.
I find relative times very useful - but that's just me - I'm only going to try and work out how long ago it is anyway. I have my satnav setup the same way - because most of the time I want to know how much longer my journey is going to be rather than exactly what time I'm going to get there. But if I went to a lot of places where I need to be somwewhere on time, then maybe I'd probably have it the other way round.
So that's the thing, some people like it, some people don't. If you can provide a setting that switches it like on my satnav then great!
I would add that relative time works internationally, everywhere in the world at the same time where as exact dates can be in different formats and timezones, and I know I'm endlessly trying to work out whether some dates are in dd/mm/yy or mm/dd/yy or whatever other format.