When working on a full-time contract you are expected to work 40h per week. A typical work week starts on Monday and ends on Friday (although this can differ if both parties agree). You’re expected to work around 8 hours each day but you shouldn't worry if you log 39h in one week and then 41h in the next week. Any larger differences should be communicated to the client. You need to make sure that the clients agrees to it.
Working over time
Remember that you are not obligated to work longer than 40 hours per week. If you want to work more than 40 hours, make sure to notify your client about that. They need to give you a green light for over time. When you work more, your client receives a higher invoice and you need their consent.
Your working hours are flexible. It's up to you if you want to work in the morning, evening or during the night. Before the project starts you agree with the client on overlapping hours. In case of US-based clients, 4-hour overlap is usually enough. In most of the cases, you need to be available between 4:00PM and 6:00PM CEST / 7:00AM and 9:00AM PDT. You can change the overlapping hours during the project if both sides agree. If your client contacts you outside of the agreed overlap you can reply in your working hours. Though if it's something really urgent, we advise to help them as soon as you can.