I use SPB Mobile Shell 3.5.1 and you can set the weather to update from every 30 minutes to 4 hours or not at all. However, the source that SPB gets it's weather from only updates once an hour. You can get SPB Mobile Shell from here:
http://www.spbsoftwarehouse.com/
I too have the large weather icon on my homescreen thanks to Mskip's ProPlus Elegance Mobile Shell enhancements which can be found here:
http://forum.xda-developers.com/showthread.php?t=566245
It is a little annoying to have the sun out on my screen when I know it's dark. I'm seeking to resolve this issue.