“在那时”的英语可以翻译为：at that time ...

就在那时，我恰好环顾了下四周。It was just then that I chanced to look round.就在那时，博物馆陷入了一片漆黑。At that instant the museum was plunged into total darkness.就在那时，房前传来一声铃。At that moment a chime sounded from the front of the house....