Existe esos parches que te dijeron, pero si lo quieres mas tiempo, exite el parche que Activa/desactiva el Sleepmode

Parche VKP;Add the possibility to enable / disable SleepMode
;Menu -> Settings -> Display -> Screen Saver -> Sleep Mode
;Works with patch "Add ability to change the retention time of illumination for each BOOK"
;(!) Shutdown SleepMode consumption will increase battery
;(c) k790Alex
;original idea by Sic, RandoM
;V1.2
;pAtChFiLe=/boot/phone_app.cxc


Solo buscalo para tu firm...