My take is that we affirm our gender to find peace, and this can be different for everyone. Not everyone needs to 'complete' medical transition as much as possible, and many find peace with social transition alone.
I lived my life with gender incongruence, and my genitals were a significant trigger for me. But I didn't really need to be functionally female down there, just visibly feminine, so I opted for minimum depth vulvaplasty. 5 years post op, I am still happy with that option.
The procedure to get bottom surgery included a 'real life test' back then. So to satisfy my surgeons criteria I socially transitioned, even though I had mixed feelings about doing it. People told me different things, from the surgery would significantly reduce my dysphoria, to the surgery won't make a difference to my dysphoria, but my experience was that it mostly eliminated my dysphoria. To the point that I considered if I had started with bottom surgery, I might not have needed to socially transition and disrupt my former life.
But everybody is different. A lot of my trans friends prioritise social transition, so opt for facial surgery, breast surgery, hair transplants, and hair removal as priorities. So the question is when do we finish transition? Well, basically it is when we find peace. For some people this will simply mean occasional dressing to our gender. Others need to completely change their lives and body as much as possible. This may also depend on the time in your life, ie, you may find that occasional dressing works in your 20's, but you need to go further as you grow older.
So there is no set beginning or end, but whatever gives us peace as individuals!
Hugs,
Allie