It does mention the M35 date.

Initially the Tyranids in The Last Ditch are thought to have arrived there some 7000 years ago- noted to be somewhat earlier than M35.

Later, they realize that those Nids are much, much older. With the "comet" that turned the planet into an iceball all those years ago, actually being the hiveship.

Necrons don't make an appearence. Nids first seen in the new codex (mawloc, tervigon) do, however.

This novel is chronologically shortly after The Traitor's Hand (specifically, 942.M41).