You don't have to create SFB3. It is incorporated in the PLC's operating system if the CPU is capable of handling it. SFC's and SFB's are system functions and system function blocks. It depends on the type of CPU if a certain SFB/SFC is incorporated or not. Check the datasheets to see if this block is present in your CPU or not.
Kind regards,
Jean Pierre Vandecandelaere