I know that, if the notebook is used for a long time every day, the computer will be overworked and liable to malfunction. But how many hours are too long?
How many hours at most can I use the notebook daily (or weekly) in order to prevent computer overwork?
Computers are meant to be used. I have on laptop that has been powered on an running various applications continuoulsly for the last 4 years. It has never had a problem. I use my work laptop at least 15 hours a day with no problems.
Notebooks aren't meant to be turned on 24/7, so my general guidelines are turn it on when you wake up and turn it off when you go to bed. That's what I've been doing with my D620 (and D610 and L400) for many years.
I wouldn't worry too much if you have a Latitude and keep it on most of the day.
Dell Latitude D620, Intel Core 2 Duo T7600 2.33GHz, 4GB RAM, 250GB Seagate Momentus 5400.4 HDD, 64MB Nvidia Quadro NVS 110M, Intel PRO/Wireless 3945 ABG, DVD±RW, Windows Vista Ultimate w/ SP1
My Latitude LM P133 has been on for at least twenty hours every day for nearly eleven years and has never had any problems.
Current (Dell Spare Parts) battery has been in its bay for over eight years and still has better than 50% of its original 'run-time'.
Was upgraded to its maximum potential in 1998 with 72 MB RAM, 6.1 GB HD and Windows 98 and has never needed any format/reload of OS.
Now semi-retired, it rides in the cabin as a GPS powered 'Air-Show' for the entertainment of the passengers.