They accept collect+, just drop it off at your newsagent for free, no need to faff with paying postage/post offices.
it is a great system and they did offer that, but collect+ do not operate on my island, do they suggested royal mail, which worked over night.
Every refund I've had has happend within a few days/a week. 4-5days IME would suggest they were about to do it as they said.
Maybe I was a bit impatient and maybe I've just been lucky in the past but never had to wait more than a day or two, including a standalone shop in Scotland with an online offer that gave me same day refund (same day the tracking number said they received the goods back).
If I want something cheep, I buy online, If I want something quickly buy in a shop.
As mentioned above, local bike shop was first call, they didn't have it in, probably because it costs too much and takes up too much space to stock all options now we have three tyre standards. They suggested it would be quicker (and cheaper) for me to order it on line rather than wait for their weekly order to come in.