Can individual SLA policies be set up for different companies?

Freshdesk has multiple SLA policies that could be set up to apply to four categories - Sources, Types, Groups, Companies, and Products. Kindly make sure you are on the Pro ( previously Estate) plan for this. 

Please navigate to Admin --> Workflows --> SLA policies --> Edit, where you can choose the option to have the concerned SLA adhered to by only specific companies, under the section Apply this to -> Companies.