With many states unwilling or unable to get insurance exchanges operational by the health-care law’s deadline of Jan. 1, 2014, pressure is growing on the federal government to do the job for them. But health-care experts are starting to ask whether the fallback federal exchange called for in the 2010 law will be operational by the deadline in states that will not have their exchanges ready. “It will be an enormous uphill battle to get this thing launched on time,” said Robert Laszewski, a consultant and former insurance executive who is watching the effort closely. “They have a Herculean task, even if everyone was cooperating.”