If i sent a 1st class letter on friday night (9pm) from london to essex when should it arrive?

Question

Do saturday and sunday not count because they are not ''working days''?

Answer 1

should arrive by monday i would say.

Answer 2

It will arrive on Monday if you posted it in an ordinary letter box (pick up Sat at 12:00).

1st class post takes one working day to arrive.

Royal Mail does not deliver on a Sunday because it's not a working day for posties hence the letter will arrive on Monday.