这里为何用进行时We were waiting 90 days ...?

CNN 10 《Uncertain Future of Popular Entertainment Venue》

When you're marketing a movie, it's a huge expense. Right? We were waiting 90 days before that movie could come out on DVD or into the home, which meant you had to market the movie all over again. 

So eradicating that and being able to pull that date up to 17 days, it means that we can grasp off of that first theatrical marketing blast if you will. 

这里为何用进行时We were waiting 90 days ...?

你断句错误。90 days并非谓语动词的持续时间状语，而是修饰before的。在离那部电影的DVD发行还有三个月的时候，大家就在等待了。而不是大家等了三个月。注意修饰语的修饰关系。