‘On schedule’ was how the Tri-City Voice described the project in August 20, 2010:
According to Bay Area Rapid Transit (BART) spokesperson Linton Johnson, the Warm Springs Extension, 5.4-miles of new BART track from the current Fremont Station to a new station in Warm Springs, Fremont, with an optional station at Irvington is “on schedule and under budget.”
An award of contract is expected in March 2011 with construction lasting from June 2011 to June 2014. Construction costs are estimated at $300M with anticipated funding of $421M. Testing of the BART extension to Warm Springs will begin in April 2014 with live service expected by the end of 2014.
And then it got delayed until 2015 (Mercury News):
Q You report that the BART Warm Springs station will open later this year. Wikipedia says early 2016. Can you use your superpowers to find the actual date they plan to be ready?
A BART says late this year  remains the target. They are testing the connections from the main Fremont station to this new station. After that’s done this fall, we should know more.
Delayed again, until 2016 (Mercury News):
With its structure nearly complete and testing of trains in its second month, the Warm Springs/South Fremont Bay Area Rapid Transit Station is expected to go into service this summer , according to BART spokeswoman Molly McArthur.
Last October, the agency delayed opening of the station on Warm Springs Boulevard near South Grimmer Boulevard from later that year to sometime in 2016. Testing of several systems such as communications, train control and traction power were expected to begin that November. However, trains did not begin rolling into the station for testing until January.
“It’s kind of like watching grass grow,” McArthur said jokingly.