Denver’s Landmark Preservation office on Friday declared Tom’s Diner potentially historic, a decision that buys community members who are interested in preserving the 52-year-old restaurant more time to save it. Denver residents have until June 7 to apply for landmark designation on behalf of the building. If the city doesn’t receive any applications by then, the restaurant will receive nonhistoric status, allowing it to be razed within the next five years. Earlier this month, Alberta Development Partners, based in Greenwood Village, applied for nonhistoric status along with their proposal to redevelop the Googie-style diner, for sale at 601 E.