The blues and jazz HAVE influenced metal immensely so I would say yes to learning those two genres first.
I can't say how long it will speed up your progression to rock/metal specifically as everyone's learning process is different! I do think it would be a great way to ease into the rock genre as that is how the greats introduced metal!
I think you will really enjoy this article on heavy metal's blues and jazz roots! Check it out
http://www.phoenixnewtimes.com/music/excavating-heavy-metals-blues-and-jazz-roots-6618861
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