When you choose "Periodic" timing mode instead of Oversample or Real Time Sampling, the PIDE adopts the execution rate of the Task that it is within as the delta-T value for the equation. That's the default, and it's what is in your program.
You can define a Function Block Diagram as the Main Routine for a Program, even though a ladder logic routine is the traditional (and default for the pre-created Main Program -> Main Routine) first routine that calls the FBD. I often have some RLL that needs to be executed as well, but if your Program is pure FBD, just assign the FBD routine as the Main Routine for the Program.
Peter's suggestion about the words "incremental" and "absolute" is well-taken. I know that when you're looking at a chemical process or flow/level control that words that belong in basic dynamics can confuse people.
His explanation about the ISA algorithm is also good, and it leads to the PIDE's support for Independent and Dependent Gains. There's nothing exotic about this; Proportional Gain is still unitless and Integral and Derivative are still time constants in units of 1/Min and Minutes.
I mentioned the execution rate because I recently encountered a system that had been running for years on a PLC-5 with the PID instructions executed every scan, and most of the time intervals set for 100 milliseconds in the instruction.
They worked by coincidence because the PLC-5 was so heavily loaded that it's total scantime was about 100 to 110 milliseconds. Some of the instructions were configured for 1 second time interval, so their tuning parameters were "way out of whack".
When we converted to ControlLogix the scantime went down to about 10 milliseconds so all the loops began overcorrecting and oscillating.
Instead of just "dividing all the gains by 10" or attempting to re-tune twenty loops during a one-hour shutdown, I moved everything to a 100 ms Periodic Task and that emulated the PLC-5 timing enough to make the system run.
The experience (and countless similar ones reported by Tech Support) made me sensitive to this basic configuration issue and even more appreciative of controllers that don't allow you to make a mistake (like the brilliant TI-505 loop solver that was separate from the logic solver).