Pink-Footed Geese in December

Hello, I am hoping to go and see the pink -Footed Geese take flight on my 60th birthday on December 15th 2024 at the Wader Watch point in Norfolk.

On the  Snettisham Spectacles 2024 Dates & Times page of the RSBP site,  it notes the dates of  21st November & 10th of December and then

again form the 21st of December to 7th of January 2025 to be able to witness this. Could someone please explain to me the gap in these dates, 

and I'm wondering that  if I were to turn up on December 15th, my birthday, would I be disappointed !? Many thanks, Paul