How long can a buyer wait before putting in an item not received complaint

[Saltire]

I posted 3 parcels last Friday. One was 1st class recorded (I was told it was too heavy to go 2nd class) and 2 others 2nd class, all recorded.

1 of the 2nd class parcels was delivered on Tuesday 1st December. The 1st class and other 2nd class ones are "still being procesed through our system for delivery".
The buyer of the 1st class item contacted me to say she hadn't received it yet. I emailed her the tracking number, but obviously she was getting the same response as me.

Can I hold on a bit longer, or should I refund her now, and then claim back from RM?

Royal Mail don't consider a parcel to be lost in the post until 15 working days from posting. I think you should hold on a while longer. Tis a bugger to claim back from RM when it involves Ebay, and you don't always get the full amount refunded to you.

ask her to go to her sorting office as it may be there - the postie doesn't always leave a card and so she may have been out when delivery was attempted

One of the buyers contacted me today to say hers had arrived on Saturday. The buyer of the 1st class item keeps sending me messages - through my actual email address, not ebay messages - saying things like "I'm waiting,I'm waiting" or "How much longer do you expect us to wait".
I contacted him - the proper way through bay messages, and again gave himt eh tracking number and asked him to pop down to his local sorting office to see if it had been left there.

Cheeky sod. Did it get sorted? I have had things take ages recently, but always asked politely. My postie is excellent but I still checked with the delivery office just in case. However, it seems anything that is being sent to me recorded is taking longer. My tracking numbers were saying the same thing. Couple of first class recorded items took over a week to get to me.