Two points... 

First, this will make it much more convenient for Cargill and other food processors NOT to hire Muslim workers in the first place.  These employees are winning the battle, but likely losing the war.

Secondly, in practice, there is latitude in the prayer times.  We visited Dubai for our honeymoon and experienced many "calls to prayer".  People generally just kept about their business and didn't stop and drop to pray.  We asked about this in a Q&A session at the Jumeirah Mosque and were told that people would pray when it was convenient for them and didn't typically stop their activities to do so.  

That said, it doesn't seem unreasonable for Cargill to have the workers' break times align with the prayer times roughly, even though the prayer times do change throughout the seasons.  I'd imagine that the workers only have two breaks per day, so that would be a limitation also.