Flow execution time measurement

[dimgiagos44]

I have created a heavy image processing flow and with golang Time module i count the execution time of the flow.
I have put the time pointers in the start and the end of the flow in the Define function. Usually the time measured is about 600ms.

But when i check the timestamps of logs, the real time taken for the execution is always above 1 minute.
What is the explanation of this huge difference??