珍惜:cherish/treasure
  把握:seize
  回忆:recall/recollect/reminisce
  怀旧:nostalgia
  纪念:in memory of/commemorate
  虚度:waste/loiter/squander/idle away
  流逝:time flies/ wear away
  延迟:delay/procrastinate
  转瞬即逝:in a blink of an eye
  千载难逢:once in a blue moon
  Seize the day.把握今天;
  Time and tide wait for no man. 时光不等人;
  How time flies!光阴似箭;
  indulges in reminiscences of 沉溺于对...的回忆;
  recollect past experiences or events缅怀过去经历和事件;
  contemplate the future思考将来