One day with 4 rounds of interviews. Not necessarily in this order: 1 (longest) technical with software architects/dev leads where you'll be drilled with questions, and scenarios to see how you think, react, and to test your knowledge of the tech; 1 work culture interview which is basically just a dialogue with members of the team you'll be working with to see if you're a good fit for them and if they're a good fit for you; 1 product/QA interview which gets you familiar with the product life-cycle and the process from beginning to end; and 1 with CTO which will also be a dialogue scenario, but he'll be quizzing you to get an understanding of your thought process - ie, brain teasers, etc.

Since you've already completed the CTO round and received an initial offer of 17 LPA, but asked for a revision to 19–20 LPA, and today’s call involves HR + Project Manager, this is likely a final negotiation + fitment discussion.