@MartinCrieffsLemon You wouldn't order from online on Standard Delivery 3-5 Working Days and then email to ask the company to send it immediately. You'd use the Next Day Delivery as that offered what you needed.
Similarly, you should ask the buyer beforehand to make sure they can meet your need rather than purchasing with a set Delivery time and then asking for quicker.
That's moot because Vinted literally doesn't offer any other options for delivery timescales, so it's less a choice and more being in a bind. So you're forced to request.
Yes wisdom dictates that you should ask beforehand. But if I haven't and I suddenly realise I need it sooner what on earth is wrong with a friendly: Hiya, sorry to be a pain, but I really need this item to arrive ideally before Saturday. Is it possible you could post it today or tomorrow morning?
If you take umbrage and get massively faffed over that and give me rudeness or a terse reply or quote Vinted shipping times to me, for even asking after I've paid money for your item, you won't be getting a good review from me, not because you refused, no, but because you are being totally unreasonable and acting like you're doing me a big favour.
A reply like: Hey, sorry but I live 3 miles away from the drop off locker/I work Mondays till 6pm or I'll see if I can, but I really can't guarantee it unfortunately.
Will be understandable and absolutely fine.