what should be the format of CDT in SFC 1?

From the System and Standard Functions manual,

System Software for S7-300/400 System and Standard Functions Volume 1 and Volume 2

27.3 Date and Time as Complex Data Types

Actual Parameters for DATE_AND_TIME

The DATE_AND_TIME data type falls into the category of complex data types, along with ARRAY, STRING, and STRUCT. The permissible memory areas for complex data types are the data block (D) and local data (L) areas.

Because DATE_AND_TIME is a complex data type, when you use DATE_AND_TIME as a formal parameter in a statement, you can provide the actual parameter only in one of the following forms:

• A block-specific symbol from the variable declaration table for a specific block

• A symbolic name for a data block, such as "DB_sys_info.System_Time", made up of the following parts:

- A name defined in the symbol table for the number of the data block (for example, "DB_sys_info" for DB5)

- A name defined within the data block for the DATE_AND_TIME element (for example, "System_Time" for a variable of data type DATE_AND_TIME contained in DB5)

You cannot pass constants as actual parameters to formal parameters of the complex data types, including DATE_AND_TIME. Also, you cannot pass absolute addresses as actual parameters to DATE_AND_TIME.

Translated from Siemens_speak, it means creating a symbolic name from the DT variable or the DB you want to use to contain the DT variable.
So if you have a DB12 that contains a DT variable called, for example in DBW0 namedsystime,open thesymbol table and generate a namefor the DB12 , such as TimeDB.
Then your CDT output (which you wan to access DB12.DBW0) would be written symbolically as"TimeDB".systime.

Hope this helps,
Daniel Chartier