Flow Scheduler

I am a new user of MultiTrans and I am experimenting with the Scheduler in Flow. I have assigned 1 assignment to 1 translator who can process 300 words per hour. According to the Scheduler this assignment should be completed in just over 2 hours. That seems correct since there are 788 words to translate.
If I adjust the productivity setting to 600 words per hour, the time spent by this translator is correctly reduced to 1 hour. But according to the overview screen this job still requires 2 hours.

Any suggestions how I can solve this?