How to Get the Current System Time using SOQL

You don't need to use SOQL. You can just create a new DateTime and set it to the current date and time like below

DateTime myDateTime = system.now();

Or if you only want the date, then

Date myDate = system.today();

Alternatively, there is a method System.currentTimeMillis() that returns the current time in milliseconds.

From that, you can create a new DateTime with the DateTime.newInstance(Long) method:

Long longtime = System.currenTimeMillis();
DateTime dt = DateTime.newInstance(longtime);

If you cannot use Apex, and need to use SOQL only, then binding is not allowed. Which means you cannot use system.now();

With that in mind, you can use Date Literals, such as YESTERDAY, TODAY, TOMORROW, and so on.

Eg:

SELECT CreatedDate FROM Account WHERE CreatedDate <= TODAY
SELECT CreatedDate FROM Account WHERE CreatedDate <= YESTERDAY