Most systems are moving or have moved to 64 bit time_t, but that doesn't actually help because the compiled timezone data files which they're still using for timezone and DST lookup are still based on 32 bit quantities. At least, that was the case on my Linux Alpha box (until it died this morning. Need PSU)

The workaround we have in SBCL sucks more than slightly, to be honest. What we'll probably do at some point is get the source Olsen data ourselves and parse it into a form that doesn't throw useful information away quite as freely.