we'll cross that bridge when we get there; we'll think about it when the time comes
Idiomatic expression meaning to deal with a situation when it actually happens, rather than worrying about it in advance.
There's no point worrying about it now. We'll cross that bridge when we get there.
What if I fail the exam? Well, let's think about it when the time comes.
Archaic kanji spelling using 其の; rarely used in modern writing.
A set phrase composed of その時 (that time) repeated with the topic particle は, literally 'that time is that time'. The exact origin is uncertain, but it is a natural Japanese expression that became idiomatic.