Antonella16
I believe you should have 28 days from the date you claim it.
So you can wait until basically the last 10 minutes before it expires to claim it.
Then you will have the 28 days to complete it.
Quite a number of times I have claimed free re-released stories right near the end of the countdown timer.
But you can only do this with free re-released stories....not with all events & special weeks.