This configuration is available in current version of MantisBT
Use setting $g_default_show_changed

I'm not sure how that variable would achieve what chillax was asking for. My understanding is that $g_default_show_changed influences how many items in the list get bolded but it doesn't show the time of those items.

Hmm, this is what documentation tells, I didn't try.

$g_default_show_changed
Highlight bugs that have changed during the last N hours. The default value is 6.

http://docs.mantisbt.org/master/en/administration_guide.html#ADMIN.CONFIG.DEFAULTS

I will check this

I am writing nonsens.
I was wrong when reading the description (reading "set the time" instead of "see the time")