I've left mine for hours and it still wakes up fine. I did Install CPU Master Free and set my min clock to 384 MHz and max clock to 1512 MHz and checked the apply at boot option. Try it and see if it helps.
Also I'm not 100% sure but I think you need to go to settings > Wireless & Networks > Mobile Networks and uncheck the Data Enabled box ??? Pretty sure I read this one somewhere. Not sure if it was for the sleep of death or if it was for another issue all together. This is for the TouchStone charger.
I did a clean install of webOS 3.0.4 then followed by a clean install of CM7v2.1 as I'm kinda anal about OS installing and updating when I have controll to do a full fresh install instead of an update.