The following sentence appeared in a paragraph. I could infer the meaning but failed to convince myself with the construction :
This is the time when we did something for our country.
It would not necessarily be unusual to hear/read a construction such as that which you posted. For example, the sentence could follow a discussion about a period of time or could refer to a photo that was used as an illustration. However, as it is presented out of context and at face value, I would be inclined to replace "This is" with "That was".