I still haven't figured out what factors determine the speed of letter delivery, in particular from Minsk to the Minsk region, but I sent it once on a weekday from this point and the letters were delivered the very next weekday.
I did the same thing at another location, and just once it was just as fast, and since letters usually take 5 days.
A normal post office.
Regular mail. But there are almost always a lot of people in the evenings. The working hours of the parcel delivery department are generally interesting: From 9-15. No working person will have time. Therefore, we have to wait with everyone in the general queue