Abstract: Personal media sharing of photos and video has become a spectacle of the immediate, yet it may come at the cost of meaning and significance. To explore this design space, we created a new tool, Postulater, that supports time-delayed photo and video sharing. Our goal was to understand how media sharing tools should be designed and how they might be used for sending media, if users were able to select delivery time explicitly. We conducted a field evaluation of Postulater over six weeks and found that participants valued sending time-based messages to send reminders, share personal memories and reflections, affect future time periods, and send social greetings. Yet these messaging acts often garnered strong emotions from our participants. The implication is that time-based messaging systems should be designed in a cautionary way that balances the need to send messages 'into the future' with complex human emotions that such practices can create.