@Yozzer i recall viewing this same CCTV clip only 2 weeks ago and on it she is walking up to the post box and she is on the phone at the time having a conversation. She is seen to post something.
Strange as you say that it has been removed.
I wonder if any other press reports have the CCTV link that we can see?
This is from my timeline for the exact period you mention that I took from when I viewed the CCTV:
14:48
It was a walk to the post office of 0.8 miles from work and would take 17 minutes and so she would arrive to post letter at approx 14.48.
If her Mother was accurate with her time of conversation, Claudia was probably talking to someone else as seen when posting the letter-who?
14:51
CL was spotted walking home and given a lift by a female work colleague, her name Jo.
This would have to be after posting the letter and by car the time to cover the remaining distance of 0.9 miles would be Approx. 3-4 minutes.
Jo dropped her off outside her home, again at Approx 14:51 (Based upon above time and distance assumptions).