You can change it by either overriding the output/friendlytime view, or by hooking into the format, friendly:time hook.

Also, by default if you hover over the timestamp it gives the exact date and time.

And there's already a plugin doing this,

https://community.elgg.org/plugins/869364/1.8.2/elgg-1819-enhanced-friendly-time

@per jensen @bret i really appreciate you!