[ltp] Maximum sleep time R52?

[m h]

How long should I be able to sleep my laptop for (and still be able to wake=
 up)?
In the two times I've tried overnight (on a fully charged battery), it
wouldn't wake up in the morning.
The only point of reference I have is a friend with a Z series who
says he always just put it to sleep (for up to a day) (note he was
also running windows, and has since moved to a mac).
The other point of reference is my brother with a T series who doesn't
sleep/hibernate at all because he says it borks on windows and isn't
reliable.

I've found sleep to be reliable for short periods <~3 hours....

comments, suggestions?

thanks

mattt