Hi and welcome,
I'll give you an explanation of how progesterone works for NBE... which in addition applies to HRT too. But, I'd add an anti-androgen and drop down the PM between 1,000 mg to 1,500mg. Or follow the program I attached below.
Firstly, ignore the advice “it doesn't matter when to apply progesterone cream”... this is completely untrue. At the start of puberty (in girls) estradiol is released which starts the formation of Breast Buds, scientifically known as T.E.Bs (terminal end buds) under the nipples and areolas. By applying or using progesterone too early interferes with that normal breast bud formation (the alveolar morphogenesis) because progesterone lowers the estradiol production thus causing an incomplete growth of breasts.
Waiting till you've developed breast buds then adding progesterone is the best way to develop your breast. Progesterone is released after a girl's first menarche (menstrual cycle, aka period).
Using the right kind of progesterone matters, the cheap stuff (the Now brand progesterone cream) has ingredients (seed oils) that causes inflammation and clogs pores, saw palmetto (which inhibit progesterone receptors). Cheaper isn't always better.
Puberty initiates branching morphogenesis, which requires growth hormone and estrogen, as well as IGF1, to create a ductal structures.
As Dr. Powers (my doctor, but I see his PA) tells it, breast development needs more E1/E2 during the first stages of development, then adds progesterone by the 3rd year (unless he's updated his position). I used PC after I developed breast buds (which was at 6 months). E1 is estriol and E2 is estradiol. And his reasoning is because of the thousands of Trans patients he's treated (with blood tests) he determined E1/E2 is essential for the first stages of breast growth… There's scientific evidence that backs his hypothesis.
I suggest this program below because it's helped many (thousands?). Each supplement has meaning and reason, take for MSM. It stimulates a certain pathway that stimulates breast growth. And this brand of progesterone cream below is probably the best brand to use (I have no affiliation with product, or any other product or device).
https://www.breastnexum.com/showthread.php?tid=24358&page=8
https://www.amazon.com/Smoky-Mountain-Naturals-LLC-Dermatologist-Tested/dp/B00EB0AQA4/ref=mp_s_a_1_1?keywords=Smoky+mountain+progesterone&qid=1703910730&rdc=1&sr=8-1
Lastly, following the female hormonal cycle for breast growth is unproductive… why? Men (or AMAB "assigned male at birth”) don't have ovaries, so we don't cycle like cis-female do. If we do cycle it's to reset receptors and detox. Ideally one could follow a 5 day plan (5 days on 2 days off).
I'll post research regarding the information I've collected and posted about the use of progesterone in another thread.
Happy New Year.