My 20-page text-only sideblog took three full days to process, so yeah, I would not expect main blogs or image-heavy blogs to take a reasonable amount of time.

The main third party tool I've seen people use is tumblr-utils, a set of Python scripts. I don't have a guide to hand, as I didn't go that route myself, but you can probably find some guides if you look under the "tumblr utils" tag there.