Here are a few things for you to look at:

Select dateadd(minute, 990, dateadd(day, datediff(day, 0, getdate()), 0))

,dateadd(minute, 990, dateadd(day, datediff(day, 0, getdate()) - 1, 0))

Now, with the above you could do something like:

Select {columns}

From YourTable

Where YourDate >= dateadd(minute, 990, dateadd(day, datediff(day, 0, getdate()), 0))

And YourDate < dateadd(minute, 990, dateadd(day, datediff(day, 0, getdate()) - 1, 0))