Construct DateTime using today's date at a specific time

SQL Server 2000 / 2005:

SELECT DATEADD(MINUTE, 30, DATEADD(HOUR, 16, DATEDIFF(DAY, 0, CURRENT_TIMESTAMP)));

-- or

SELECT DATEADD(MINUTE, (16*60) + 30, DATEDIFF(DAY, 0, CURRENT_TIMESTAMP))

-- or

SELECT CONVERT(DATETIME, CONVERT(CHAR(9), CURRENT_TIMESTAMP, 112) + '16:30');

SQL Server 2008+:

SELECT CONVERT(DATETIME, CONVERT(DATE, CURRENT_TIMESTAMP)) + '16:30';

SQL Server 2012:

SELECT SMALLDATETIMEFROMPARTS(YEAR(GETDATE()), MONTH(GETDATE()), DAY(GETDATE()), 16, 30);

Probably the easiest thing to do is to cast the current date/time to a date (stripping the time off), cast it back to a datetime to allow use of datetime's overloaded + (plus) and, finally cast your desired textual time to a datetime. As follows:

select cast(cast(sysutcdatetime() as date) as datetime) + cast('16:30' as datetime)

returns (when run on 11th Jan 2018):

2018-01-11 16:30:00.000