The IITM BSc Data Science Program has a very flexible structure. It has 3 terms a year and has no mandatory attendance; rather, attendance is measured through the submission of weekly assignments. According to the institute, the estimated time required to do fairly well on the course is around 10 hours per week which is an achievable goal for students who are already enrolled in another degree program.
The program is designed to be accessible to as many people as possible and the only strict requirements are the in-person, proctored exams that students have to write at centres near them. The list of exam cities can be found here.
The BS program is offline, but, there are avenues for students to occasionally use the IIT Madras campus. Students with a high CGPA can utilise study halls within campus or even register for offline elective courses whose credits can be transferred to their program. Both options have limited seats based on availability.
Once you complete your four-year BS degree, you are not automatically eligible for any postgraduate degree at IITM as these degrees often have an admission test such as GATE, CAT, JAM, etc.