Depends on how similar the domains are. Stacks are vastly different in companies working in disparate domains -- I've worked as a software engineer in C4ISR, gaming, EDA, oil & gas, HFT, remote sensing, consumer electronics, and more. The stacks couldn't be more different & foreign from each other. Like living in different universes. Six months to learn all the moving parts is about right.

(I can't imagine a career in only one domain; how boring would that be? Hopefully will be getting a new job in HPC soon.)