If you select a font that is not monospaced, the letters in the lower center of the screen will dance. :)
(https://i.imgur.com/8ByeJqe.gif)
Odd, it looks like the characters are moving with the time.
Many otherwise proportional fonts keep their digits monospaced to avoid such issues. It is also very important for presenting tables of (usually right-justified) numbers. I've never heard of a programmatic solution to this. Just use a font with monospaced digits.
Simutrans might have to do something about the fact that the hours switch between one and two digits. If there is no such thing as a space character that is the same width as a digit, then padding with zero is the only option.
r9309 will not have dancing middle text anymore.