BuddyPress.org

Which comments are you talking about ?
Blog comments ?
See here: https://codex.wordpress.org/Function_Reference/comment_time

To do this, If you use BP 1.2.8, go to bp-themes/bp-default/functions.php or better to the functions.php of your child theme

In file there is a function bp_dtheme_blog_comments
Near line 78 change
`

to this

`

how to embed this function into your theme’s function ? read here:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/how-do-you-do-this/