Average time spent on site

[#1]

Average time spent on site in Omniture site catalyst and Average time spent on site in Google Analytics are showing extremely different numbers. Please give us a feedback of why they are so much different. 

Omniture Sitecatalyst : Average Time spent on Site (07/24/2011) : 15.33

Google Analytics : Average time spent on site (07/24/2011) : 4.37

Thanks, 

Gan

[#2]

Ditto. Totally different numbers.

[#3]

Per Google Analtyics for March: 00:01:35 Avg. Visit Duration

Per SiteCatalyst: 5.07 Average Time Spent on Site