This partly depends on what your students have done before they begin their IGCSE course. If they have been in your school for some years beforehand, then you may have been able to begin building up their knowledge and skills already. If they come to you from many different backgrounds, then you may need to do more work with them to prepare them for IGCSE.
IGCSE syllabuses are designed on the assumption that students have about 130 guided learning hours per subject over the duration of the course. ‘Guided learning hours’ include direct teaching and any other supervised or directed study time. They do not include private study by the student. This figure is for guidance only, and the number of hours required may vary according to local curricular practice and the student’s prior experience of the subject.
You should try to have one relatively long session each week, so that your students can carry out practical work.