Timeout entering username/password too short

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I just installed Fedora 23 on a few machines (Gnome desktop). When getting to the greeter screen asking for username and password, the timeout for it is set to something between 10 and 15 seconds, before the screen goes dark / no signal. This is annoying, could it wait longer ? I have hunted for an answer for a good while, and played with tools such as gsettings, dconf-editor - no clues on this.

This also happened with Fedora 22.

Any hints ?

Thanks