the previous 2 answers are right. It's a holdover from the nickel battery days. Read you equipment manual. Those that I have (for cameras, phones, etc) have never mentioned the 8-hour / overnight charge. With the intelligent batteries and chargers necessary for Lithium based batteries, you'll see that charging stops once the full-charge is detected anyway - that doesn't take anywhere near 8 hours.
As an ex-techie, I hear lots of howlers from salespeople (normally spoken with a degree of unjustified authority and experience too!). It lets me know which ones I should not trust