just a note: Trevor mentioned a 3 months boundary for the whole translation, but considering the difference between extensive and intensive magnitudes this information doesn't give a full value.. it would be helpful for the volunteers to know what's the number of (unique) strings to translate .. some experiences from our current translators (Tech) could also help here...
What do you exactly mean? How much time does it take? Difficult to say, as I did not take an account of dedicated ours to that. For sure, if you do the work more intensively, you'll be faster: the translation terms are in your mind, you caught the technical meanings, the homogeneity is easier.
Checking the spelling and grammar is a must have to have a good work.
I suggest to work with the GUI (Passolo) as well with the help files. One makes the other clearer and help on translation work.