In bookkeeping notebook, the variable `an_hour_ago` is actually doing a_day_ago

[stuartcampbell]

an_hour_ago is defined as now - 60 * 60 *24 which is a day ago

Link to the notebook: https://github.com/bluesky/tutorial/blob/master/Let%20Us%20Do%20the%20Bookkeeping%20For%20You.ipynb