I much preferred the F4 for tripod work over the F100 because you can just see what every setting is nice and easily. The F100 turned itself off too quickly for me too.
Just curious---did you change the custom setting #15? stock meter off time is 6 sec. but with the CS15 you can change it to 16 sec. That might fix your problem. You can also still download a PDF of the manual form Nikon USA.