HALF (TIME) IN GERMANIC LANGUAGES

With English for a second language and Spanish and Valencian as my mother tongues, as well as general expertise in Romance languages, I still have this confusion with the Swedish "halv" and German "halb" used in clock-time expressions. As a child, as a teen, I could not understand how "halv sex" referred to 19:30, one hour later, while Sweden, Germany, and so forth share the same timezone with most of the European Union...
The snag is that not only Germanic languages (sans English, which took the "half past" surely from French influence), but also Slavic and Fenno-Ugric ones, use orientation points as time periods named by an ordinal number (“the 6th hour”, i.e. 5:01–6:00). Ordinal time indicating is well-known especially from Russian, which consistently has “10 of the 6th hour” (desjat’ šestogo) for 5:10, and so on. But it occurs also in German, especially with half hours (halb sechs for 5:30), though German does not use its ordinal numerals here. This distinction leads to another universal:

(5) Ordinal time periods are always full hours.

Thus, no language has something like “5 minutes of the 2nd half of the 6th hour” for 5:35.

In Russian, this system is quite thoroughgoing: minutes, quarters, and halves can be used in ordinal indications, but in southern German, only quarters and halves can be used in this way. So is it in Swedish and other Scandinavian languages. Other German varieties allow it only for halves. 

Icelandic

Á sjöunda tímanum í kvöld (The seventh hour)
- This means 18:01-18:59, it's within an hour, not a specific time

Hungarian

fél három (with no suffixes, litterally "half three") = 2:30
negyed három (lit. "quarter three") = 2:15
három negyed három (lit. "three quarter three") = 2:45

The western Slavic languages (as already told by Jazyk and Koniecswiata): 

Polish: Wpól do trzeciej (lit. half to third) = 2:30
Czech: Půl třetí (lit. half of third) = 2:30
Slovak: Pol tretej (lit. half of third) = 2:30

The Polish version seems to be the most logical, as it is perfectly undestandable: "half an hour to the third hour". It's interesting though, that the western Slavic languages use ordinal numbers in this case. The same use of the ordinal for clarifying occurs in Russian, Slavic as well... but not in Germanic languages ("halb drei", "halv tre", etc.) or Fenno-Ugric ones ("fel három"), which use cardinal numbers to refer to ordinal time periods. That is the reason for so much confusion.

But, having grown accustomed to systems that use cardinal indications for the time (ie Romance languages and English) since childhood, old habits die hard and someone saying "halv fem," "halv sex..." or its equivalents in other languages still leads me to confusion.