Leaked documents indicate Uber plans to go public within 18 to 24 months, and one analyst wonders why the company is waiting so long.

“I’m surprised how long they’re waiting, actually, that they don’t consider themselves ready to go for some reason,” says Kathleen Smith, principal of Renaissance Capital, a manager of IPO-focused exchange-traded funds.

At the beginning of the year, speculation was rampant that Uber and other major players in the tech startup world would go public before the end of 2015. The recent $50 billion valuation of the company fed anticipation, though Smith at the time said she still thought an IPO would still be a little way off. Uber declined to comment.  

Reuters reported Friday that the company was projecting a three-fold increase in bookings to almost $11 billion for 2015, yielding an estimated $2 billion in revenue.

The figures are based on a confidential slideshow prepared by Chinese bankers and Uber that was leaked to the news agency. The documents also pegged the IPO window as well.

Smith says the projected $2 billion in revenue shows “impressive skill and is going to bring a lot of attention to its IPO by investors.”

And waiting 18 months or more would certainly be long enough for Uber to IPO after what she described as the current “major meltdown” in the global stock market wanes. Recent tech IPOs, like Twitter, are in particular ailing, notes Smith. Twitter shares dropped below $26 Thursday, the price at which shares were set when the company went public in 2013.

Smith cautions, however, that the reported IPO window is also far enough away that Uber’s valuation could drop. Which raises the question: Why is Uber waiting? Maybe it isn't ready for the scrutiny that comes with going public, Smith says.

Matthew Wong, a research analyst with venture-capital database CB Insights, told Inc. earlier this month that the scrutiny public companies face might not work well for a company like Uber that is still in the position of challenging regulations in the areas where it operates.

The company is still in a phase of expending a lot of resources in new markets, like India, without making a lot of money in those places, he said. 

"It's not surprising to hear that Uber is targeting an 18- to 24-month time frame for IPO," Wong said. The company faces competition abroad from Ola, Didi Kuaidi and GrabTaxi, all backed by deep-pocketed investors. Staying private to meet these challenges before facing quarterly earnings pressures makes sense.