Summarize:

At minimum, you will need to record the location and intended opening date on paper, digitally, and in a secure location. If you keep a calendar, set reminders each year, or schedule an email to be sent to you on a certain date. Consider writing the location and opening date in your will, or leave a letter with a grandchild containing instructions. If your time capsule is intended for retrieval years or decades after its original placement, make doubly sure that several people know of its exact location and surroundings. Ask them to hold the information for safekeeping, passing it along if necessary. Take photographs of your placement, identify GPS coordinates, and write down all data important for relocating the precise location. Register the time capsule to make it feel more official, and give the capsule a higher chance of being found if all else fails. Even if it is just a painted rock, keeping some kind of visible, yet not overt, sign of the spot to dig for the capsule will help you or someone else in the future avoid losing the treasure.
Do something to remind yourself or others about the time capsule. Make extra arrangements for a time capsule that will outlive you. Place a marker of some kind on the exact site of a buried capsule.