using cookies - best way to do this?

[gBay]

hi,
im building a site for a few doctors surgeries. the user is able to see what appointments are available and then book that date/time. i have a table (in my db) of dates/times and a checkbox to say whether the time has been booked or not (and display only times that havnt been booked). i was going to have the user add the time to a "cart" and then check the "booked" checkbox in my db when theyve paid for that appointment. but if i have lots of people looking at the site at the same time, then they may be able to see times that are just about to be booked. i think a better way is to have the date/time stuffed into a cookie which expires after 5 minutes. so when a user adds a time to their "cart", it will say something like: "this time will expire in 5 minutes until you book it or re-add it to your cart". does that make sense?
how can i do this with server-cide cookies (im using jscript)? can anyone think of a better way to do this?
many thanks

[bbolte]

sounds reasonable...