Answer: Run the following query and it will give you the date of SQL Server Installation.

SELECT create_date
FROM sys.server_principals
WHERE sid = 0x010100000000000512000000

Question: I have installed SQL Server Evaluation version. How do I know what is the expiry date for it?

Answer: SQL Server evaluation period lasts for 180 days. The expiration date is always 180 days from the initial installation. The following query will give the expiration date of evaluation version:

-- Evaluation Version Expire Date
SELECT create_date AS InstallationDate,
DATEADD(DD, 180, create_date) AS 'Expiry Date'
FROM sys.server_principals
WHERE sid = 0x010100000000000512000000
GO