Most contracts I've been involved with define a day as 7 or 8 hours. This is almost never going to be solid programming time though, as you will need to commun

Most contracts I've been involved with define a day as 7 or 8 hours. This is almost never going to be solid programming time though, as you will need to communicate with the client, handle documentation and other tasks which legitimately take up part of the 8 hours. Also, you should take at least 1 or 2 breaks during the day which shouldn't be included in the 8 hours. By the end of the day, you're not going to be programming as effectively as you were at the start. This is just the nature of working 8 hour days; the client won't expect you to be a machine. If you're really concerned about this, try to do all the difficult thinking and planning at the start of the day, leaving more straight-forward tasks for when you're tiring. In short, say you'll work 8 hours and just do your best.