I think stuff like this, HDR too, really just comes down to preference
That being said, I do think it is important to start placing hint brushes and area portals during alpha.
Preference, sure, but detailing stuff in early alphas is in some ways a waste of time since you probably have to do it all over again at some point due to layout changes. No map is perfect in a1/a2 states. Same with HDR: most lighting is very basic in alpha versions so there is no need for HDR.
And yes, optimizing should be done from the minute you start mapping on a new map. Start with basic area separation, and then get into the details. But never wait until further on in the map's development, it will cause you a lot of trouble, and since it's not exactly a fun thing to do mixing it in with the detailing and layout stuff early on provides a nice base to work from further down the development cycle.