深夜 and 早朝: late night and early morning
Distinguish late-night and early-morning periods and read dates across a schedule.
Late at night
深夜 (しんや) means late at night. 「深夜に帰宅しました」 says that the speaker arrived home late at night.
「深夜まで作業しました」 says work continued until late at night. Do not interpret it as starting work then.
Early in the morning
早朝 (そうちょう) means early morning. 「早朝の公園は静かでした」 says the park was quiet in the early morning.
「早朝に出発する予定です」 describes a plan to leave early in the morning. A plan is not a report that departure has already happened.
Checking the date as well as the time
「深夜に着いて、翌日の早朝に出発しました」 places arrival late at night and departure early the following morning. 翌日 specifies the date relationship.
Late-night plans can cause date confusion. Asking 「何日の何時ですか」 clarifies both date and time beyond these broad expressions.
Is 深夜 the starting point in 「深夜まで作業しました」?
Show the answer and why
No. With まで, it marks the late-night endpoint up to which the work continued.