Hi Kumar! Firstly, let me tell you, there are two categories of placement that take place in B-schools - Summer Placement & Final Placement. Summer Placement is conducted for the first year students where they spend around four to five months doing internship in a company. The companies pay stipend to the students. After the completion of the internship tenure, they go back to their respective B-schools to complete the second and final of their MBA/PGDM. 

The final placement is conducted for the second year students and these are full-time jobs and there is no duration constraint unless the company signs a specific year wise contract. The duration of the service tenure would depend upon the employer and the employee and HR policies.