You must live in a very backward part of the country, SP48. I can't find any Post Offices around here that close at 5.00pm!
I've just checked on the hours of Post Offices in my area. The one in our small town (of under 5000 people) is open from 9.00am to 5.30pm six days per week. (That extra half hour during the week might not seem much but it's a boon to people who work 9 to 5).
The main one in the larger town 3½ miles away has similar hours, except that it opens half an hour earlier (at 8.30am) on Mondays and Thursdays, to assist those collecting pensions or benefits. (A smaller branch in the town is also open to 5.30pm, except for 12.30pm closing on a Saturday).
The village Post Office 4 miles in the other direction is also open to 5.30pm (except on Saturdays, when it closes at 1pm)
The village 5½ miles away has a Post Office branch open 7 days per week, from 7.00am to 8.00pm (except on Sundays, when it closes at 6.00pm)
Other (very small) villages have a mobile Post Office calling there several mornings per week, with one tiny hamlet even having a Post Office service which goes to their homes. (Admittedly that's only once per week, but it's still providing a valuable service).
Those services are all much better than we had until a few years ago, so perhaps the Post Office is moving with the times after all?