就在 + 这时
这时 (zhèshí) is a time noun meaning "at this moment" or "just then." It is used to mark a specific point in a narrative when something notable happens. The phrase 就在这时 (just at that moment) adds emphasis and is a common storytelling device.
我正准备出门,这时电话突然响了。
wǒ zhèng zhǔnbèi chūmén, zhèshí diànhuà tūrán xiǎng le.
I was just about to go out when the phone suddenly rang.
就在这时,一个陌生人走了过来。
jiù zài zhèshí, yī gè mòshēngrén zǒu le guòlái.
Just then, a stranger walked over.
天渐渐暗了下来,这时路灯也亮了。
tiān jiànjiàn àn le xiàlái, zhèshí lùdēng yě liàng le.
The sky gradually darkened, and at that moment the streetlights came on too.