Die Zeit wird kommen, da Sie dies verstehen werden.

English Translation

The time will come when you understand this.


The time will come when you are going to understand this.

The second part is also Future in German.

Furthermore, “Die Zeit , da” is a little bit old-style and grandiose. The whole sentence sounds like being from a 19th century prophecy.

“That will be the day when the light shines on thee.” (Not a translation but to give you an idea of the style.)