Answer: hourglasses

AnswerCrossword Clue
HOURGLASSESTimepieces
HOURGLASSESTimers for ostrich eggs?
HOURGLASSESThey show the passage of time
hourglassesShaped like such a device
hourglassesHOURGLASS, an instrument for measuring the hours by the running of sand through a narrow neck
hourglassesAn invertible device with two connected glass bulbs containing sand that takes an hour to pass from the upper to the lower bulb