Talking out my hint with a detective, here's the unraveling so everyone is on the same level:
There is one actual hint:
The first day echoed around the world. The second was important only to me.
It has a clarification:
What kind of event reverberates (echoes)?
So we know that there are two days. One was an event that reverberated/echoed around the world. It happened recent-ish - much less than 100 years. (It's also not referring to 9/11). The second is something that means anything really only to me. We also know that this second date has not passed yet, and that it does refer to when my outcome grows.
If the second date refers to when my outcome grows, there is a logical conclusion about what the first date may indicate.
And then here's something new: I'm careful with my diction. I used 'echo' very purposefully, because it's one of my favorite words to indicate a desolate mood.