Extend the Execution time of workflow

How can we extend the timeline of running workflow in temporal?

What do you mean? By default, the workflow duration is not limited. So you don’t need to extend it :).

We have a timeline of 7 days . The workflow exits after that. We have a use case in which we are supposed to extend the ttl+3 days if the new action is triggered by user . Suppose if the user wants to initiate the pay later flow , since he has opted for paylater flow . we need to keep his workflow active of atleast three more days

You can write workflow code to block for seven days unless a new signal is received. When a signal is received, the sleeping interval is reevaluated, and workflow is put to sleep again.

How exactly to do this is SDK specific. Which SDK are you planning to use?