Correct.
- Half to the second (halvanden, still in use today) = 1.5
- Half to the third (halvtredje) = 2.5
- Half to the fourth (halvfjerde) = 3.5
- Half to the fifth (halvfemte) = 4.5
And so on. You might notice that I sometimes write it like "halvfemte" and other times "halvfems". The latter is just the way it was spelled when used in a combined word (another fun quirk in Danish that we inherited from Germanic this time!). 90 is today spelled just "halvfems".
Yeah, it's kinda the difference between saying "the clock is currently half past twelve" (the English way) and "the clock is currently half to one" (which we say in Danish and probably in a wealth of non-English languages too).