When the chinese readings of first 10 days are used?


Usually japanese readings are used for the first 10 days like ついたち、ふつか、etc.

Japanese wiki [here](https://ja.wikipedia.org/wiki/7%E6%97%A5) shows readings
like ごにち, ろくにち.. (You can just change the number in the url before the 日 to
navigate). So are those used anyhow?




いちにち is always used instead of ついたち to refer to a duration "one day".

> 仕事を一日【いちにち】で終える to finish the task for one day

ににち～じゅうにち are much rarer, but can appear as part of phrases like [二、三日]{にさんにち}
or [五、六日]{ごろくにち}. I don't think 二日 by itself is ever read as ににち.

References:

  * [Homographs: how to deal with them?](https://japanese.stackexchange.com/q/3435/5010)
  * [How to read: the "~" (tilde) in "3~4 行"](https://japanese.stackexchange.com/q/21679/5010)
  * [How to read 二、三日](https://japanese.stackexchange.com/q/25776/5010)

