Horde Session Timeout
You can keep your session active by configuring Horde to refresh your inbox automatically every x number of minutes. In Horde, open the "Options" menu, then select the "New Mail" option. Select one of the options under the "Refresh Folder Views" drop down box then click the "Save Options" button. Finally, make sure the webmail windows displays your inbox so it can be refreshed from time to time.