Yes, if you set realistic goals with sufficient breaks in between study sessions. It is much better to know exactly what you want to achieve every day (in the form of a list or timetable) and tick off everything as you do it- more motivational than just deciding to 'revise today'
Yes, I would say they are, just make sure you make them sensibly, not sectioning off 15 hours of study for example. Or you could make a weekly plan instead e.g. Tomorrow I will make sure I understand osmosis, do a quiz on active transport and make a mind map on cell differentiation (if you wanted to focus on biology)