hour() returns the hour component of a Datetime in the local time zone of the context user.

Sample Code:

trigger CaseTrigger on Case (before insert) {
    
    Boolean tomorrowTargetBool = system.now().hour() >= 12 ? true : false;
    for ( Case c : trigger.new ) {
        if ( tomorrowTargetBool ) 
            c.Target_Date__c = system.today() + 1;
    }
    
}

In the above example, if the case is created after 12 PM, the target date field will be next day.