generally 4-8h incubation is enough for mammalian cells to be transfected. Changing media after 4-8 hours helped us reducing cytotoxicity. Hope it may help you too.
Titer the lipofectamine reagent preparation, figure out the minimum volume of reagents to carry to optimum plasmid or anything for transfection to achieve maximum efficiency.
Point the recommended volume of transfection reagents cause huge death even if you keep for 4-6hr. In 4-6hr you may see death but after overnight, cells die.
That only, try to lower down the reagent volume, its works, many people work with lower volume. Otherwise, look for other brands which have low toxicity.