This is a screen of the workflow:
I can give you 2 easy options:
Set SecurityManagerApprovalTime to the Workflow Context: Date and Time Started variable. This is the date and time when the workflow started which should work if the workflow starts when the security manager approves/rejects.
Assuming the workflow is started on SharePoint list items and the approval action is modifying the items, then you can use the Modified field of the items to get the date and time.
If none of these work for your scenario, in order to help please provide more details about how the security manager approves and who and when starts the workflow.