Do mormons have a doctrine of afterlife preaching and repentence?

I swear I read somewhere some years ago that Mormons have a developed doctrine of saints in the afterlife descending to Hell in order to preach the gospel to those who are stuck there and give them the opportunity to accept Christ and repent. I find this interesting and appealing because it would neatly solve the age-old dilemma of the dude in the jungle who went his whole life without ever hearing the Gospel. He ends up in Hell, but the friendly mormon missionaries take a holiday from heaven to come and hang out with the damned where they "preach to the spirits in prison". This jungledude then has the opportunity to accept the gospel. Presumably there is no time limit set on the offer of salvation and therefore it is safe to assume that everyone will eventually end up responding positively to the gospel (either here on earth or after death in Hell). My question is, is any of what I just said accurate? Do Mormons actually believe anything similar to this? (I note that what I just described is slightly similar to the "Holy Saturday"/"Harrowing of Hades" tradition in the Catholic/Orthodox churches: this is where Jesus "descended to Hell" and busted out of hades/sheol all the righteous people from the old testament times) (Can someone please add the tag "harrowing-of-hell" or "holy-saturday" (these are basically synonymous))