After reviewing other posts and testing web client login time, for DS Auth systems, in different environments (using DS User accounts and domain), we can confirm that it requires about 4 seconds to 10 seconds.

LF Cloud login time is ~ 500ms.

Are there any steps we can take to reach a ~ 500ms goal with DS Auth?

Any modern computer processor should be plenty fast enough to achieve this goal. Bus speeds are faster than ever. Networks are faster than ever. There really is very little limitations on the hardware side anymore.

Reference of another post where someone is finding 5 second login times even with reverse DNS configured.

https://answers.laserfiche.com/questions/128658/Windows-authentication-performance-with-Web-Client--90x-slower-vs-Windows-Client#170009