I have had a customer contact me something that was posted Monday 7th 1st class has not arrived yet it was a large letter i have asked them to wait a few more days
Yes I’d defo say there’s still time for it to arrive as at the best of times first class takes 1-3 days and Royal Mail don’t consider anything sent standard post as missing until 10 working days have passed.
I posted one the same day 1st class recorded delivery at the same time just checked the tracking and that has not been updated since it was posted on Monday
might be worth using special delivery