Originally Posted by
Prospero
There are several VAT Refund Desks at BLQ. The airside
Travelex Desk at BLQ opens at 05:30. It is located next to gate 15. Is this a viable option?
Those desks are for passengers who already had their VAT forms stamped by the customs and who want to receive cash. The OP's issue is that the customs office opens after their flight boards; but since they're not leaving the EU from BLQ it is not really a concern.
