If you are planning to use ETL link Informatica or snap logic, you can schedule bi-directions sync using the ETL.
If you wanted to implement on your own, you can use SOAP API from Salesforce and Use any other API to connect to SQL server. Schedule your code execution by using any Schedule options.
Note: - Maku sure you sync only the unmatched data to avoid overhead.
To do real-time bi-directions sync between Salesforce and SQL server (https://skyvia.com/data-integration/integrate-salesforce-sql-server) I recommend you to use service like Skyvia. With help of it, you can easily set-up synchronization, literally in few clicks and without any coding at all.
If you are planning to use ETL link Informatica or snap logic, you can schedule bi-directions sync using the ETL.
If you wanted to implement on your own, you can use SOAP API from Salesforce and Use any other API to connect to SQL server. Schedule your code execution by using any Schedule options.
Note: - Maku sure you sync only the unmatched data to avoid overhead.