I won't argue whether we do too much or too little. We certainly give too much, (now retired because of that). Just argue carefully, especially if the person asking you to come in early is the one controlling the budget. Might be time to look for a days contract in a nearby town instead of a stipend only. I gave a lot of time but I learned early on my start date and end date were set in stone, (as far as my school was concerned though I did usually work 1 or 2 days right after school was out). Start date was especially set in stone.