How long does it take for Google Instant answers to recalculate (high profile website)

Maybe until the next ice age.

Why would google put your site there because of traffic
or some lame marker like alexa?

Besides, most of the time, it's not going to put your
website there. It's going to give an answer that it
gleans from it's data gathering.

The traffic you get would be next to nil. I have my
question answered, done and done.

Paul

As I said, we are 1st organic result for those queries, so it would make more sense in my point of view to extract from our pages rather than 2nd, 3th or 4th organic result.

In any case, instant answer for those queries will just send traffic to the source, rather than people stop looking, since those are specific queries where people are looking for detailed answer. It's not like 20*60 or 2 pounds to kg.

I'm monitoring up to 60 queries and for 2 queries we came as instant result in less than 2 days after the last change, but for remaining queries, it is still using other websites as before.

What I've seen from page cache, some of our pages are updated in 3 days time so we cannot expect fast propagation of instant answers.

If it doesn't propagate in 2 weeks time, we'll do one change in structure of the website and continue doing changes until it starts to use our website or we gave up.

Nobody is going to have an answer for you. Google has never released any information about your question and very little info about how they pick the answer for those queries.