How to record video from Blackmagic using ffmpeg?

Question

bash

There is a task to organize video recording according to the schedule through ffmpeg. But it is very critical that the recording starts exactly at the appointed time, for example at 09:00:00. The duration must also be precise, such as 60 minutes 00 seconds.
With the -t switch signed, it sets the encoding/writing duration. This solves the file length issue. However, I don’t understand how to prepare ffmpeg so that it starts recording exactly at the appointed time, because it only starts starting at this time and it turns out that the start of recording is shifted by 1-2 seconds. Actually, the whole question is, is it possible to fix this?