you are "established" in holding at the instant the "to-from" indicator flips or the adf needle reverses direction. You are established in the airspace alloted to you for holding. Note we are not using the term "established" in the personal sense that you, the pilot, have established your self comfotably in the holding pattern. You have entered the airspace - that's what ATC wants to know.
The timing of your inbound leg would begin as you roll out on heading with the needle coming into center in a good turn - however, when that does not happen, it requires some judgement. What if your turn undershoots the radial, and you roll out early to intercept? You are still going inbound - better time it.
What if you overshoot badly and the needle goes full scale the other way? You turn to an intercept heading, but you are still inbound, better time it. Think about why you are timing. You want to fly outbound a certain time so that the inbound will be one minute. But, if you have not established the proper crab angle on the outbound, the inbound under/overshoot will change the timing, so, untill the crab is worked out, the time will be off anyway, but you still need to get some kind of estimate by starting the inbound time when you are approximately coming inbound. The quality of the inbound time is also dependent on the quality of the timing of the outbound leg. Starting at exactly the same place and adjusting when the crab angle changes.
The whole purpose of timing is to stay within the assigned airspace - that's all. How you do it is your business - except when you are training or checkriding. Then it is however your instructor or examiner wants you to do it.
That's my story and I'm stickin' to it.