Is there anyway we could set a activity to expire itself? or cancel a process after certian leadtime.
After a certain lead time in an action, an action overdue gets thrown for that specific action.
Instead of creating a condition in the transition, create an exception like shown in the below screenshot and select the action overdue option.
You can create a transition from the desired action to a RAISEEXCEPTION action which will cancel either certain actions or the entire process.