Puzzling use of progressive form


In this sentence:

> 僕は両親が帰ってくるまで公園で時間を **つぶしてい** なければいけなかった。
>
> I had to kill time in the park until my parents came home.

Why does 時間をつぶす need to be in the progressive form? Why can I not write
...時間をつぶさなければいけなかった。

I'm assuming 時間をつぶしている is progressive here. It certainly isn't habitual and I
can't see how it would work as change of state. Thanks.




It doesn't need to be progressive, つぶさなければ works as well.

There's not really big difference between つぶしていなければ and つぶさなければ here. I think
it's parallel to "had to be killing time" and "had to kill time".




It doesn't need to be progressive, つぶさなければ works as well.

There's not really big difference between つぶしていなければ and つぶさなければ here. I think
it's parallel to "had to be killing time" and "had to kill time".

