I know that yonaka is considered to be during the middle of the night. Are specific time periods involved?
This dictionary defines
夜中 as, among other things,
夜のなかば - literally "middle of the night". Much as in English, there is no firm definition of exactly when the "middle of the night" is. Ultimately a person's interpretation is going to depend to some degree on their lifestyle, opinions, and many other things.
That said, according to an investigation the NHK did a while ago, it seems like many people think of
夜中 as starting at 11 PM and ending at 3 AM.
Note: see here for the investigation original text. It literally says
午後11時台～午前2時台, but my assumption is that
午前2時台 encompasses the period of time between 2 and 3 AM and consequently the entire period of time ends at 3.