Twelve Hours

The other evening my husband and I came home from an evening out and there was a message on the answering machine. It was from an elderly woman that he volunteers with. She said she was not coming in to work that day as she overslept and her alarm never went off. We were a bit confused until we figured out what happened. She must have gone to take a nap in  the evening and awoke at 7 o'clock. Since it was light, out she thought it was 7am but it was 7pm. Her alarm never went off because it was 12 hours too early. She did not realize that it was night and not morning. I wonder how long it took for her to figure out that her time clock was off.