If you want history of your activity , you can activate history in user parameters .
User parameter->display history

It always on yes.
But when deveopper change state of activity, perharps from "recorded" to "in progress" and from "in progress" to "done"
I'm not able to know when it is done.

In bellow a snapshot of global user parameter

Thank

You have activate display history in Global Parameters.
Go in user parameter , you have the same parameters ( display history ) , say "yes" for display history .
When display history is activated , go in your activity.
In the down of your activity you have the history ( see attachment ) .
And on this history you can show update of status for example

It's possible that, the "real work time allocation" is deducted by the changing history ?
If a developper pass the activity from "in progress" to "done" , the system automatically calcul the time and consider it as "real work time allocation".

No, system would not be able to guess exactly time really spent on activity (reallity is often different from estimate) , and even if we concider transforming planned into real, system cannot guess when work was spent (today, yesterday, , before)