Using 間 without particles

Question

In an IMABI tutorial showcasing the differences between 間 vs うち, the author notes:

Again, it is possible for 間 to not be followed by a particle, but this is not possible for うち.

and then uses the following sentence as an example:

家に帰るまでの間、雨につかまってしまった。

I was caught in the rain till I got home.

Question: Isn't this just an example of a particle being omitted (but still there, implicitly) from 間? That is, isn't this just "家に帰るまでの間に" or "家に帰るまでの間ながら"? If this is the case, couldn't we just convert sentences like

知らないうちに、眠ってしまっていた。

into

知らないうち、眠ってしまっていた。

to get them "particleless", as well?

If not, and there really is zero particles in the original sentence (implicitly and explicitly), then does that mean 「家に帰るまでの間」is functioning purely adverbially there?

Answer 1

It is rather about addition of に. 間/うち is a noun and X間/うち can be used adverbially as noun phrases expressing time (like other time expressions). You can think に is optional to some extent, but idiomaticity varies depending on the nature of the main verb (and other semantic factors).

As for 間/間に, に adds the 'point-in-time'-ness to 間 which sounds like the whole duration. When there is に, the main clause tends to be instantaneous and when there is no に, it is continuous.

• 家に帰るまでの間、小説を読んでいた

Reading a novel happens all the time while going back home (on the train for example).

• 家に帰るまでの間に、小説を読み終えた

Finishing a novel is instantaneous.

In both of the above, switching 間/間に makes them less natural (but not completely odd).

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Similarly for うち/うちに, but the difference seems more subtle to me.

• 本を読んでいるうちに、眠りに落ちた
• 本を読んでいるうち(に)、眠くなってきた

For the former, dropping に is ok but less natural (to me); for the latter, に is totally optional.