This will be something you should discuss with you professor. For most summer positions, it is expected or delineated in the grant that you will spend around 40 hours a week (8 hours a day, 5 days a week) in the lab for around 10 weeks. During the school year, depending on the level of commitment and stipulations of research-for-credit, around 10-20 hours will be spent in the lab. For many types of biology research, you will be working in the time frame of your organism or experimental procedures, and thus your time frame may be unusual since it is dictated by these factors.
Finding a Research Lab: Getting your hands dirty or very clean