can the client set up the cookie property, accept cookie but expires quickly?

[searain]

i am using cookie to set up the language choice and the products information.

it works fine on all other people's browsers except one client claimed that

he can set up the language (he choose the english) and get the products info (shopping cart) right for a while, and suddenly, all these cookies lost. he will be set back to the default language which is dutch, and he lost the shopping cart info he was working on.

and then when he try to get back to reset the language (which is a cookie and use the shopping cart (which is also cookie), he cannot do it anymore.

what is the problem?

by the way, could it be because the clock on his computer set up wrong and expires the cookie (I set up the cookie to be expired after 24 hours)? the cookie time is based on the web site and his computer or only based on his computer?

thanks