The Civil Aviation Authority (CAA) refund programme for Thomas Cook customers will now open on 7 October, despite originally being scheduled for 30 September.
The CAA has also confirmed to Which? that anyone with Atol protection will have up to one year from the date of the travel agent's collapse to lodge their claim.
Thomas Cook customers patiently waiting for the online claims system to open today have been expressing their frustration on social media this morning.
Approximately 360,000 Atol-protected future Thomas Cook holidays that have been cancelled are due to be refunded - the biggest Atol refund programme ever, according to the CAA.
UK CAA chief executive Richard Moriarty said: 'This will be three times larger than any refund programme we have managed before, and we are implementing new systems to enable us to process these refunds as quickly as possible.'
If yours is one of the 100,000 bookings paid for by direct debit, the CAA has said it will aim to automatically refund you within the next 14 days.
This means you won't need to fill in any forms, and the money should enter your bank account without you having to do anything. But you may need to make a separate claim for any deposit you paid when you first booked your holiday.
For bookings made by all other payment methods, you'll need to fill out an electronic refund form using the online claims system on the CAA website, which is now scheduled to launch on Monday 7 October.
The CAA advise that you keep hold of all your paperwork in preparation for submitting a claim.
The UK Civil Aviation Authority launched the largest peacetime repatriation on 23 September 2019 to bring more than 150,000 people back to the UK.
In the first seven days of 'Operation Matterhorn', 106,000 Britons flew back - this accounts for more than two thirds of the total number of those abroad at the time of the collapse.
Today (30 September), 53 flights are scheduled to return a further 8,000 people as part of the repatriation effort.
Operation Matterhorn continues until Sunday 6 October, with nearly 1,000 flights planned in total.
Repatriation flights will only be operating until 6 October 2019.
After this date, if your holiday is Atol protected with Thomas Cook, the CAA will make individual arrangements for you to return to the UK with existing flights on other airlines. Details of this will be sent directly to you.
If you booked a package holiday through Thomas Cook but your flight is with another airline, it may not be affected and you may be able to travel home on this flight as planned.
However, other elements of the package, such as accommodation and transfers, will be affected.
If your holiday isn't Atol protected, you will need to make your own travel arrangements, including booking your own return flights.