Question

this is /was a time when从句用什么时态

Answer 1

this is a time when +一般现在时/ 现在进行时
this was a time when + 一般过去时/过去进行时
a time 是指“一段时间/时期”；when 引导的是定语从句，修饰a time

Answer 2

朋友，应该是：
1 There is a time when I have to depend on myself for a living(一般现在时)
2 There was a time when I had to depend on myself for a living (一般过去时)

Answer 3

It is the time that 后面用过去式，虚拟语气。
It was the time that,少见。

Answer 4

过去时态。