<schemalist>
  <schema id="org.gnome.desktop.session" path="/desktop/gnome/session/">
    <key name="idle-delay" type="i">
      <default>5</default>
      <summary>Time before session is considered idle</summary>
      <description>The number of minutes of inactivity before the session is considered idle.</description>
    </key>
  </schema>
</schemalist>

<schemalist>
  <schema id="org.gnome.desktop.session" path="/desktop/gnome/session/">
    <key name="idle-delay" type="u">
      <default>5</default>
      <summary>Time before session is considered idle</summary>
      <description>The number of minutes of inactivity before the session is considered idle.</description>
    </key>
  </schema>
</schemalist>

Change org.gnome.desktop.session/idle-delay type from "i" to "u"
Change org.gnome.desktop.session/idle-delay type from "i" to "u"

It can't be negative.
