内(うち)にWhile, During

とき expresses the time of an action or event, like 'when' in English. It can be used with nouns as in 雨の時 'when it rains', verbs as in 父が帰ってきた時 'when Dad came home', or adjectives as in 暑い時 'when it's hot', and can describe one-time or repeated actions. うちに means 'while' or 'during,' often with the nuance that it's the ideal or only time to act, e.g. 熱いうちに食べてね ('Eat it while it's hot.').

Both patterns can express the idea of 'while,' but differ in nuance. ているあいだに refers to something happening during another ongoing action. For example, 勉強しているあいだに電話がかかってきた means 'The phone rang while I was studying.' うちに emphasizes doing something while a particular state still lasts. For example, 早いうちに帰ろう means 'Let's go home while it's still early.'

ているところだ conveys that an action is in progress at that moment, with the nuance that the speaker is occupied with it, e.g. 晩ご飯を食べているところだ ('I'm in the middle of eating dinner.'). In contrast, うちに describes doing an action while a certain state is ongoing, often with the nuance that it's the ideal time, e.g. 熱いうちに食べましょう ('Let's eat it while it's hot.').

ながら attaches to verb stems to express performing one action simultaneously with another, e.g. 音楽を聴きながら走る 'listen to music while running'. In contrast, うちに can follow various words or phrases to express doing something while a certain state or condition persists, e.g. 若いうちにマラソンを走りたい ('I want to run a marathon while I'm young.').