Sayge's damage buff says 5% but in reality is anything from 1-10%. This buff says 10% but despite having more than 100 strength, I did not get 10 extra strength, only four. Tooltips are often wrong in this game. This is one of those instances. Yes, only five minute duration, and since it only happens for five minutes on the hour and queue times can be longer than that, it's not an especially useful buff.
Also, in Zangamarsh you can get a five minute buff that adds 30 to all stats, and it actually does that. You just need to get the KB on a neutral sporebat. Probably not soloable for most classes. Hunters might be able to. This next part is kind of vague, but I remember killing some red slimes in one of the Cat zones that gave me a buff on the KB too. Pretty sure that one said 10% also. Not sure of the duration. 5-10 minutes.