The character value is trimmed of leading and trailing pad characters and handled as a string literal in the declaration of an INTERVAL string literal.
Character-to-INTERVAL conversion is supported for CHAR and VARCHAR types only. The source character type cannot be CLOB.
The contents of the character string are converted to a valid INTERVAL, if possible. If not, an error is returned.
You cannot convert a character data type of GRAPHIC to an INTERVAL string literal.