Actually, let me look it up on the JP forums to make sure it's not backwards.
Edit: Read through a few forum posts (native) and it's probably more like this:
日没（にちぼつ） Formal/technical | Used in reports, timetables 日の入り（ひのいり） Also formal, slightly softer | Used by official sources like 天文台 日が沈む Casual/natural | Very common in speech
I included the last one because someone said that 「友達と日が沈むのを見に行った。」felt the most natural in a casual context.
A rough translation of what another person said:
日没 and 日の入り mean the same thing - the moment the sun goes below the horizon. However, if the sun is setting but still shining, you should use 夕陽 or 夕日
