Speciation is really a judgment call. We don’t really have objective criteria that says “99% or more genetic similarity is the same species”.
But that assumes that there is evolution happening in the first place. Plenty of organisms are quite happily living in the same form as they did hundreds of millions of years ago. The nautilus, for example, evolved about 500 mya, and remains largely unchanged today (though many of its siblings are extinct, and the nautilus itself is endangered). For simpler organisms, you can probably find examples much older.
Edit: forgot to answer your question directly. It could be never.