BuddyPress.org

Hi, as I’ve been caught out in the past by modifying core functions, I’m trying to get everything laid out correctly. I’m looking to alter the member last active date to a maximum of three months, this can easily be achieved in two lines within the bp_core_time_since() function, but what I’d like to know is how to replace that function with one in a custom functions file. Short of creating a new function as well as replacing the bp_member_last_active() function in the bp_members_template file as well, how can I keep the same structure and simply replace the function? Any thoughts?