Creating a timestamp

How can I set a field to automatically store the date and time when a progress bar reaches 100% but to stop changing. I currently have a code field cb_jumpstart_completed_step3 where I want to store the timestamp of when the progress bar cb_change_plan_points_bar reaches 100% (using CB Core Fields Ajax Update on cb_change_plan_points_bar). This is the code:

date_default_timezone_set('America/Vancouver');
$datetime2 = $cb_jumpstart_completed_step3;
$datetime1 = date('m/d/Y H:i:s');

if ( [cb_change_plan_points_bar] == "100" and $cb_jumpstart_completed_step3 == "") { return $datetime1; }
else { return $datetime2; }

It works fine until cb_change_plan_points_bar reaches 100%. However, after 100% has been reached, every time I refresh the profile page the timestamp changes to the current time. I would really appreciate your help with this.

I'm guessing you're using Update On on a Code field? Code fields have no storage. You need a place to store the timestamp. Code fields just take your PHP, execute it, and display the results. What you'll likely need is to use CB Auto Actions to store the timestamp to a datetime field.

Global
Triggers: onAfterUserUpdate
Type: Field
User: Automatic
Access: Everybody
Conditions
1: [cb_change_plan_points_bar] Equal To 100
2: [cb_jumpstart_completed_step3] Equal To 0000-00-00 00:00:00
Action
Field: cb_jumpstart_completed_step3 (I assume this is a datetime field)
Value: [cb:date format="Y-m-d H:i:s" /]
Translate Value: No