The holiday season, which is by far the most important time of year for retailers, highlights the increasingly intense battle between physical stores and online websites. Given the large number of casualties this year — witness the bankruptcy filings of such venerable institutions as Toys ‘R Us, The Limited, H.H. Gregg, Gander Mountain, Payless Shoes, and RadioShack, to name but a few — retailers must finally wake up to the core terrain over which they’re fighting: customers’ time.