I do need to estimate how much time do people spend on Stack Exchange sites on creative activities, like adding questions or answers, maybe even comments.
Probably there is a big correlation between the post size (including the number of reviews).
Still, from Data Explorer there is no way of getting this data. I can assume that Google Analytics could help here but still, I am not sure if you can get this information out of it, and also I do not have access to it.
Mainly, I could say that the time-effort could be estimated like this:
For questions: the time spend between pressing the ask question option and when the question is saved (that will have to extended if the question have multiple reviews, as it is comment to revise it few times even very soon after adding it).
For answers, I would say it is between when the page is accessed and when the answer is saved (same rule for revisions like before)
I am open to other alternatives, as long I can come out with some numbers that I can use. The best it would be if I can find a formula for estimating the time based on the size in bytes.