(Pre-existing) Indeed.  We could at least use sizeof("literal") - 1 and move half the computational cost to compile-time.
Also: "Fri Oct 1 1:1:1 UTC 2010" looks like a valid date to me, and is shorter: are we sure s has always been generated by something that uses two-digit hh:mm:ss ?  It's entirely possible there are good grounds to be sure, but they should probably be documented here !