那时候
nà shí hou · HSK 2
at that time
⏳ 那 (that) + 时候 (time/moment) = at that time
那 marks 'that' (distal demonstrative), 时 means time/hour, and 候 means moment/period. Together 时候 is the common word for time-point, so 那时候 literally reads as 'that time-moment' = back then.
那 — 邑 radical 阝(right) + 冄 phonetic
Originally referred to a place name in ancient China, with the right-side 阝 (city/region radical) indicating a settlement and 冄 providing the sound. Over time it lost its geographic meaning and was borrowed as a demonstrative pronoun meaning 'that' or 'those'.
时 — sun 日 + temple/measure 寺
Originally a phono-semantic compound: 日 (sun) gives the meaning of time or season, while 寺 (shí) supplies the sound. Early forms used 之 as the phonetic before 寺 replaced it. The core sense 'season, time, hour' has stayed stable since ancient Chinese.