Execute the following Microsoft SQL Server Transact-SQL (T-SQL) script in Management Studio (SSMS) Query Editor, SQLCMD or other client software to find out how many days the server is operating:

USE master;

SELECT ServerName=SERVERPROPERTY('ServerName'),
InstanceName=SERVERPROPERTY('InstanceName'),
DaysUp = datediff(day, login_time, getdate())
FROM master.sys.[sysprocesses]
WHERE spid = 1;
GO