Change of status from L1A to H1B with new employer?

I am currently on an L1A visa with employer X, completed five years. I plan to apply for the H1B FY2025 lottery with new employer Y. If it gets approved, will my five years (with previous employer X) of L1A be captured in the initial six-year approval period of H1B (with new employer Y)?
So, will I have only one-year validity?

What if I take consular processing leave in September 2024 on an L1 visa and re-enter the US with a new H1B stamp(Employer Y)? Will it help to capture the complete H1B six-year duration?

Yes, unless you leave the US and come back after a year of cooling period, then you can claim the remainder period of H1B.

Ideally you should request your current L1A employer to file a green card for you which can be processed much faster being in L1A that may qualify for EB1.

Alternatively if you have an approved I-140, you can request AC21 extension of status on H1B beyond the 6 year term without the 1 year cooling period.