When does Dropbox request token expire?

When does Dropbox request token expire?

I am creating a request token and the authentication url when pressing one
button,
and then a different button (from another app) is making the
authentication itself
(getting the request token and url as parameters , opens web page(the
url), and obtains access token + secret using the given request token)
But I always get an exception that the session has expired.
It only works when it all happens one directly after the other, but not
when it's split up like that.
Is there a way to modify the expiration time? Or maybe a completely
different way to overcome this issue?
I don't think I can create another request token in the second button in
the other app, because then the url won't match
Maybe holding something like session in web?