Availability of LAG function

Scenario:

Request 1

Event 1

Request 2

Event 2

Event 3

Desired Outcome:

TPT 1: Request 1 - Event 1

TPT 2: Request 2 - Event 2

TPT 3: Request 2 - Event 3

So as we want to calculate the TPT btw the event and the last request we wanted to know

In a calculation rule, LAG returns an activity that precedes the current activity by a given offset.