Tricky question, the default settings for Google's content experiements are a 2 week duration with a confidence level of 95%. If you got low traffic volume, these confidence levels may not be reached, because of differences in user behaviour on different days of the week (weekdays vs. weekends).
Even if you implement a full 100% traffic split, the testing suite may shift traffic volumes to different variants trying to find confidence levels and thus be able to declare a winner.
A/B testing does not route the first visitor to variant A and the second to variant B. Instead it's trying to segment types of traffic to be able to compare them. I have never seen a A/B test where traffic was split exactly 50% (between two variants), no matter how long the experiement was running.