I usually set the time zone on my servers to UTC, but that makes it a bit confusing for me when I use irssi. If you have perl support built into irssi, you can run these commands to alter your time zone within irssi only:
/load perl
/script exec $ENV{'TZ'}='(nameofyourtimezone)';For example, I'm in Central Time, so I'd use:
/script exec $ENV{'TZ'}='CST6CDT';To update the time in your status bar, simply /whois yourself and you should see the updated time zone. If you want more handy irssi tips, look no further than irssi's documentation.

If you're starting an application in bash and want to set environmental variables for it, you can use something along the lines of:
Thank you, this was very useful.
Madrid EspaƱa :
/script exec $ENV{'TZ'}='UTC-1';