Majority of data center users replace their gear within 3-5 years. There are outliers, of course, who replace hardware with each generation or those who run their servers into the ground, but 3-5 years is far more common, so 4 years on average.
This rough math means if AMD takes half of the new CPU orders, they should have about 10% server CPU market share within a year, consistent with some analyst estimates [1]
[1] https://www.digitimes.com/news/a20190328PD200.html
