US Admiral Davidson in 2021

https://www.defensenews.com/pentagon/2024/05/07/how-dc-became-obsessed-with-a-potential-2027-chinese-invasion-of-taiwan/

https://en.wikipedia.org/wiki/Davidson_window

A number of defence & geo political papers in the years leading up to that contributed to that testimony to congress.

China friendly SCMP suggesting 2030 (in 2018)

https://www.scmp.com/comment/insight-opinion/united-states/article/2174705/why-china-will-wait-until-2030-take-back

There's defence industry papers on it but searching on the phone is too hard, if I remember i'll have a dig from the PC when I get home