time zone change

I got mail at work today informing me IT would be rebooting my Windows
workstation to allow its timezone update to take effect.  Apararently some
OSes tie that kind of information to the account.  Don't ask me; I just
work there.  

Meanwhile, back at my apartment, it occurs to me that maybe my zoneinfo
directory needs updating, courtesy of the US congress?  What's the best
way to go about that?  

Also, I haven't found out when the zoneinfo database is consulted.  Is it
read into memory at boot time, or are changes to the file effective
immediately?  

Many humble thanks.  

--jkl