Google executive Marissa Mayer is the third person to be named CEO of Yahoo this year — and she won't have a big window to prove herself.
Mayer, former vice president of location and local services at Google, spent 13 years at Googleand was involved with Google's search, gmail and Google news features.
Despite Mayer's impressive resume, though, she will still have her work cut out for her at Yahoo , Colin Gillis of BGC Partners said Monday on CNBC's Fast Money.
"She needs to come in and prove herself," Gillis said. "Obviously Marissa is very well-known, but she's still going to be new as a CEO and we're going to have to see where she is going to take it."
Mayer will have about 100 days, if that, to prove that she is right for the job, Gillis said.
Gillis said he gave Yahoo stock a target of $20.
Mayer will start her new position at Yahoo on Tuesday and took to social media Monday afternoon to share her enthusiasm for her new job.
"I'm incredibly excited to start my new role at Yahoo! tomorrow,"
She also updated her bio on Twitter, adding "@Yahoo!" below her Twitter handle. However, a link to her Google Plus page still remained on her Twitter page. (Check out some of the Twitter reaction here.)
Beyond her initial excitement, Mayer is going to have to come out with a strong statement soon about her plan for the company to assure investors she is up for the job, Gillis said.
Mayer's appointment as CEO was unexpected, as it was largely speculated that the interim CEO Ross Levinsohn would be appointed to the position.
Investors were more familiar with Levinsohn and investors will want to see him stay with the company, Gillis said.
"If they can keep Ross in the company, that will be a real coup," Gillis said.
Leadership at Yahoo has been rocky over the last two years, with multiple people taking the chief position at the company only to have limited success in turning the company around.
Former Yahoo CEO Scott Thompson led the company for less than six months when he resigned in May over a controversy regarding his academic credentials.
During Thompson's time as CEO, the company made moves to restructure.
Yahoo announced in April that about 2,000 employees would be let go and a reorganization plan was laid out that was supposed to help the company operate more efficiently. The company said the changes would help curb Yahoo's costs by $375 million annually.
Tim Morse served as an interim CEO before Thompson, following Carol Bartz time as CEO.
Bartz served as CEO for two years (2009-2011) and although she also employed lay-offs and attempted to restructure, she had little success. She was fired in September 2011 for not turning the company around.
Yahoo's stock rose in after-hours trading, topping $16 a share.
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