Ideally, if everything turns out well, then Craig will be returning for a final time in Shatterhand
I think Shatterhand is the right direction to go in with Bond 25. I'm assuming that you're suggesting Blofeld escapes death at the end of Bond 24, but is tracked down in Bond 25 under that catchy alias [Dr] Shatterhand.
That's exactly what i was just saying above with my idea for Bond 25. But that would make it a continuation story with many of the same players involved. In this scenario i think a 2 year is fine, since much of the pre-production will be in mind, if not underway throughout the SPECTRE production.