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