If you really want to have fun with spoken German time formats, you have to get into the quarters though.
For example:
8:15 / 20:15 can be said as Viertel nach Acht (quarter past eight) or Viertel Neun (quarter nine)
8:45 / 20:45 can be said as Viertel vor Neun (quarter before nine) or Dreiviertel Neun (three quarters nine)
And I think the difference in those is regional, so those are actually more "controversial" then using 12 or 24h formats.