The translation of "five-thirty" in German is "halb sechs", which phonetically sounds hilariously similar to the english phrase "have sex." It's like saying half of six. See this for yourself by finding this translation on Google Translate and playing the audio of the German translation at a high volume. The door is now opened to a whole new world of communication possibilities with this phrase. Your application of the term is limited only by your healthy, twisted imagination. Likely the best way to use this phrase is in communication with fappalicious babes, in order to confuse the shit out of them while suggesting coitus between the two of you. If she happens to go home and look up the meaning of five-thirty in German, she will likely "get" what you were saying to her, and perhaps react in a highly favorable way (being amused and/or turned on) or in a very unfavorable manner (being offended and pissed off). Obviously, if you say this to random chicks you won't have to interact with again, you don't have to worry about their later reactions, unless of course she knows German, then you'll have an entirely different story. You can also say "halb sechs" to confuse people in a different way. Your welcome and have fun! :p
"Hey girl, you wanna hook up later and German five-thirty?"
"This guy walked up to me and said that someday we were gonna german five-thirty. Whaaa??"
"Your mom likes to german five thirty with me."
"Where the FUCK would you be if not for GermanFiveThirty?!"
"Thank the WombRaider for German five thirty."
"When Bruce Wee attempted to German Five-Thirty with Latrine Fapinwhacker, he failed to perform and was deservingly humiliated."
"What time is it?"-"German five-thirty!"
SPEAKERS:"HALB SECHS!" YER MUM:"WHAT?!" YOU:"THEY SAID "FIVE-THIRTY" BITCH, GET YOUR MIND OUT THE GUTTER AND QUIT INTERRUPTING MY GERMAN LESSONS!"
"Hey, I'm Vag Bashington and the time is German five-thirty, so hoe, that shirt is becoming on you, if I were on you, I'd be cumming on you, too!"