It takes at least 4 hours to scan ALL of the pages of a manga book, 1 to 2 hours to rotate the images for readability purposes and add to those hours the possible watermarking. 3 to 4 hours if you're feeling nice and want to adjust the Levels of the scans so they'll look solid. That is if you're working with RAW English scans already. ;x
For translations, they take weeks, depending who you're working with. If you're solo-flight and know Japanese like a native, you'll only need three to six months (not included here your school days/RL stuff) to translate a RAW Japanese Volume.
Basically translating takes years, depending on your loyalty/priorities for it. A chapter alone takes months, as far as I can see it. This is the reason why it's rare for people to translate the Pokemon manga and just wait for the English version to come out.
A little FYI for those who are complaining in this thread here.