Time is running out on Daniel Murphy in his attempt to be ready for Opening Day. The Mets second baseman was limited to taking “a couple” of swings yesterday as he deals with stiffness in his right rib cage area. It marked the second straight day Murphy was unable to participate in a minor league game, after playing defense and running the bases on Friday. If Murphy doesn’t begin playing exhibition games by the weekend, he won’t be ready for Opening Day, according to manager Terry Collins. “If he’s not back in a game you’re down to seven days,” Collins said. “And that’s not a lot of time to get somebody who hasn’t done anything all spring, to get him ready.” Jordany Valdespin played second base yesterday and would be the Mets’ starter there to begin the season should Murphy and David Wright open the year on the disabled list. If Wright were ready, Justin Turner would be the front runner for second base, provided his sprained right ankle responds within the next few days. Turner was walking on the ankle yesterday after sustaining the injury on Saturday fielding a grounder at third base. “The biggest thing for me was when I got out of bed this morning was to see if it felt stiff,” Turner said. “And it felt fine.”