> you can just start by writing down start and end dates of each chunk of work in your process

End date is usually easy: "when someone closes the ticket" but maybe "when it was released" is better?

I have trouble determining the start date though. Some ideas: "When the customer reported it", "when the ticket is created", "when someone planned a release date for the ticket", "when the ticket was commit to in a sprint backlog", "when the ticket is assigned", "when the ticket was assigned to the one who finished the ticket", "when someone clicked on 'start progress'".

Each possibility comes with its own kind of noise and some requires additional discipline.