Improve search queries based on datetime

This is heavily work in progresss and the content will most likely
change.

lib/scoped_search/query_builder.rb

@@ -146,22 +146,30 @@ def datetime_test(field, operator, value, &block) # :yields: finder_option_type,
       # but the field is of datetime type. Change the comparison to return
       # more logical results.
       if field.datetime?
-        span = 1.minute if(value =~ /\A\s*\d+\s+\bminutes?\b\s+\bago\b\s*\z/i)
-        span ||= (timestamp.day_fraction == 0) ? 1.day : 1.hour
+        if value =~ /(\d{1,2}:){2}\d{1,2}/
+          span = 1.second
+        elsif value =~ /(\A\s*\d+\s+\bminutes?\b\s+\bago\b\s*\z|\d{1,2}:\d{1,2})/i
+          span = 1.minute
+        elsif timestamp.day_fraction != 0
+          span = 1.hour
+        else
+          span = 1.day
+        end
+
         if [:eq, :ne].include?(operator)
           # Instead of looking for an exact (non-)match, look for dates that
           # fall inside/outside the range of timestamps of that day.
           negate    = (operator == :ne) ? 'NOT ' : ''
           field_sql = field.to_sql(operator, &block)
           return ["#{negate}(#{field_sql} >= ? AND #{field_sql} < ?)", timestamp, timestamp + span]
 
-        elsif operator == :gt
+        elsif span == 1.day && operator == :gt
           # Make sure timestamps on the given date are not included in the results
           # by moving the date to the next day.
           timestamp += span
           operator = :gte
 
-        elsif operator == :lte
+        elsif span == 1.day && operator == :lte
           # Make sure the timestamps of the given date are included by moving the
           # date to the next date.
           timestamp += span