It takes a little bit of time for getting used to the idea
It's fine, except you want a purpose infinitive (to get used to ...) instead of a gerund complement. Take can take a gerund, but not in this particular configuration.
- Skiing takes some getting used to.
- Skiing takes some time to get used to.
- *Skiing takes some time for getting used to.
So it should be
- It takes a little bit of time to get used to the idea.
This is, by the way, an extremely complex sentence. The part you're asking about mashes three different idioms together (take = require; a little bit of; get used to) in a very complex pattern with a very specific sense.
The diminutive quantifier in the middle (a little bit of) is just a matter of the speaker turning the volume down, in saying that the amount of accustomization (= getting used to) that something requires (= takes) is small. I.e, it's not that difficult.
That's just the first part of the sentence, note. What it takes some time to understand turns out to be the idea of a function that cannot actually be evaluated at any specific point. Which is enough to give anyone pause, given the usual definitions of function.
This Noun Phrase has
- an abstract noun describing
- a function with a special property
- which is described in a passive clause
- with an indefinite subject,
- containing a modal auxiliary (can) and
- containing a negative (not)
- which are conjoined and have overlapping scopes.
That's quite a lot of complexity for such a small sentence.
Though that is the way mathematicians talk, all right.