I don't even worry about applicaiton date vs activation date, because I worry about other posisbilities:

Do they count purchase date or posting date? (And what if the merchant post-dates the purchase?!? )

Do they mean post to the website within X months, or post to your statement within X months? (If post to your statement, it's actually less than X months, because it has to be on your statement that closes before X months are through.)

There are very few reports of people waiting until the very last moment and reporting their results. (Most people don't want to risk losing the bonus just to be a good FT guineau pig!) But that's exactly what you'd need to know "for sure" how it works at each bank.

And since I most definitely am more interested in getting the bonus than being an FT guinea pig, I only sing up for spend offers that I can comfortably do in the alloted time, and then I do complete them plenty early enough on the most conservative and paranoid interpretation possible (so that they post to the monthly statement that comes out before the X months from the application date has passed).

I guess one reason I'm paranoid is that I churn Citi more than any other bank (in part because it has the cards that can be churned most frequently), and Citi is known for counting days incorrectly! If they err in one direction on the "60 day" count (between pairs of applications), which they do, they're likely to err in the other direction on the spend threshold end date!