Hi Nipun,
This is a quite big question in an area that we in R&D are aiming to improve in upcoming releases of IFS Cloud.

As a ground rule:
The only entity that we can and that we will be able to plan and execute on are the Work Task (planning can of course be done on for example the Work List on a PM, but then the Work list is to be seen as the predecessor of a Work Task).

Today the Permit (and any Isolation Orders connected to the Permit) is connected to the whole WO (not individual tasks).
That would be something for us to look into when improving this area.

The way to in some way achieve what you want would be to create an inital task on the WO, that would represent the Establisment on the Isolation Order.
On that task you can plan and report resources, materials etc and these cost can then be invoiced as normal.
Then create an end task on the WO, that would represent the Re-Establisment on the Isolation Order.
Again, plan and report as normal.
These tasks should then have a dependency to the second task (from the first task) and to the second to last task (from the last task).
Thus stopping the start of the second task before the first task is done (Establisment is done) and to stop start of Re-Establisment before the task before that has been done. You could of course also create tasks after the “last” task for any work needed after Re-Establisment 

This would be my take on this with the current functionality.