This is an hourly charge. The less experienced you are, the longer it will take. To record 5 minutes of audio, it usually takes one of my V/O artists about 15-20 minutes.
I can confirm it. The ratio between 1:3 and 1:4 (produced minutes/minutes of work) it's normal when you have a good text. I was able to keep this ratio also making voice over syncronized with video and original voice (but not dubbing, just documental films).
The hourly charge here in Poland for "normal people" (i mean no famous voices) it's around twice the rate for simultaneous interpreting, so it's good payed.
Also, keep in mind that translating for voice over is very different that translating something that will be written and not read aloud. You have to translate for the ear.
CML wrote somethings VERY IMPORTANT. If you will do the translation you must chech if it SOUNDS good (first problem) and if you have to keep your voice inside some time limit, if it's possibile to produce this text, speaking, inside this time limit, without losing the "beauty" of the speaking..
These are things very very difficult to explain to the customer..