as long as you have three consecutive hours of sleep and you take your temperature at the same time then there shouldn't be a problem. The thing is that many times, we feel like to go to toilet at around 5am or 6am and we suppose to take our temperature at 7am then we have to hold on to it until we take the temperature before we can go to toilet. I guess it is better not to drink so much water before we go to bed so we can avoid situation like that.