Bouce rates and time on site questions.

What do you guys consider a good user "time on site"? I know this can vary drastically by the niche and type of blog/site. I have an authority site on a hobby and just offer tips and information. My average user spends about 1.5 minutes before leaving my website. I am unsure if this is a good number or not. I also seem to have a terribly high bounce rate of 78%. I have tried every trick in the book to lower that number, but have only been able to drop it a few percent. I get a fair amount of traffic from facebook but mostly from Google. My question is- Are these standard numbers for an information site or not? I am also interested in hearing how my numbers might compare with similar sites. Thanks