I think its generally 24hrs, but just count it as a day as you will be sleeping for a fair part oif the 24 hrs anyway, for example UP day for me yeterday, last had something to eat at 9.30 last night, so strictly speaking I could eat at 9.3o tonight but today is a DD so I won't eat until I have brekkie tomorrow morning. some do 6pm till 6pm etc but it all gets a bit confusing then, you just have to do whats right for you, but 24hrs is the time frame yes x