TL;DR: You must pay the IFI by the deadline indicated on your tax assessment notice. The tax is due thirty days after the date on which the tax roll is put into collection.
The payment rule
The IFI is due thirty days after the date on which the tax roll is put into collection.
The date to respect
Your tax assessment notice specific to the IFI indicates the amount to be paid as well as the payment deadline. This is the date that determines the due date applicable to your situation.
Where to check the deadline
Check your IFI tax assessment notice: the date on which the tax roll is put into collection and the payment deadline are mentioned there.