Simply use compilation time set to the DS3231 RTC.
Please do not reset after upload until upload another program.
Check available font list
magick -list font
Generation Preview
magick -depth 1 -font Courier-New -pointsize 20 label:"_0123456789_" -crop 120x16+12+4 font_2x.png
magick -depth 1 -font SpotMono-Bold -pointsize 30 label:"_0123456789_" -crop 180x24+18+13 font_3x.png
Generation Header Code
magick -depth 1 -font Courier-New -pointsize 20 label:"_0123456789_" -crop 120x16+12+4 -flip -rotate 90 font_2x.xbm
magick -depth 1 -font SpotMono-Bold -pointsize 30 label:"_0123456789_" -crop 180x24+18+13 -flip -rotate 90 font_3x.xbm