How to set addtime(current_timestamp, '15:00:00') as MySQL timestamp column default value?
MySQL does not support functions in column default values. CURRENT_TIMESTAMP is the closest thing you'll find to an exception:


  The DEFAULT clause specifies a default value for a column. With one
  exception, the default value must be a constant; it cannot be a
  function or an expression. This means, for example, that you cannot
  set the default for a date column to be the value of a function such
  as NOW() or CURRENT_DATE. The exception is that you can specify
  CURRENT_TIMESTAMP as the default for a TIMESTAMP column.


http://dev.mysql.com/doc/refman/5.5/en/create-table.html#id850368