I had this concern last week and did a chat with customer service. They said the Barclayscard didn't need to be charged within the 30 days since the purchase was booked when I ordered on 10/27. FWIW, I had the same timeframe and my MBP is PFS as of Wednesday but still hasn't shipped. Hopefully, your machine is coming soon as well.
Good to know. I'm in the same boat and my 30 days expires on the 8th of Dec.