www programming

For phpBB, all the settings you tell me were already there.

But for WP, i didn't understand where should i set that ?

there is no setting about this into admin WP config, these are advanced options that need to be setup manually in case into wp-config.php file (i assume).
Sorry but instead of another question ... you didn't answer to my question. What happen if you do the above?
Link to your site?

Sorry, i didn't understood the question, but now i do.
I made the test : i set 60s (the minimum) and i've not been disconnected.

hello, so you result logged in, after you've check remember me login into phpBB and executed the login.
Now, this mean all is working about cookies, that are setup by phpBB as a remember me login that will persist for long time (as long, as you have setup it in phpBB i assume).
With login done into phpBB full forum page, and coming into WP, now when the session expire you're logged out?
You should not, or something into WP side fire the logout code somewhere (that is very strange), or your phpBB maybe have not correctly setup the value into Security Settings -> "Remember Me" login key expiration length (in days):
set to 0 if it is not.
This is very strange that session expire if you are logged in correctly and so you have a valid cookie that each time page load, renew session if expired. Let know.

Yes, that's exactly that.

But whaterver if i am on WP-Side, or phpBB Side, i'm disconnected for the both when it happens.