The option will be available through adCenter online or through the adCenter API (version 8). It’s seen at the ad view level where keywords are connected to ad copy.
When advertisers select “rotate ads more evenly” there will be no time restrictions on how long the ads may rotate evenly, so advertisers will have plenty of time to test different creatives and see what performs best against their goals.
Google recently dealt with something of an outcry from the marketer community, after changing its options so all ads auto-optimized themselves after 30 days. After hearing from advertisers who said they needed more time to judge the performance of creative, the company changed the default setting to 90 days, and it now allows advertisers to make a special request to keep their creatives rotating evenly indefinitely.
It would appear that Microsoft has learned from Google’s misstep.