I suspect quite a few people did modify cgminer to do scrypt+salsa20/8(N,1,1) before the coin launched.  The surprise change to scrypt+chacha20/8+Keccak(N,1,1) at the coin's launch would've prevented any of them from working though and caused a bit of surprise (I was one of the people that had already modified cgminer ahead of time, thinking it would be scrypt+salsa20/8).  Due to the surprise change, it's unlikely anyone other than the original developer would've been able to prepare an actual working GPU implementation days before release.

I currently suspect a lag time of somewhere between 13.5 hours and 24 hours after the coin launched before the first YAC-specific cgminer might likely have been up and running (not including the original developer's own possible GPU implementation, which we won't know).  The 13.5 hour figure comes from mtrlt (author of Reaper and the OpenCL kernel everyone else uses for scrypt) own reported time to implement, and he's likely to be fairly high on the totem pole of OpenCL talent in the community.