The “day grid” is the grid that shows up in your Calendar when you are looking at your Calendar in “Day” view and "Week (Column)" view. The day grid will show times in regular intervals for a specific length of time. See an example below:
When you have Day Grid turned on, the times for your events by default don't show. If you'd still like to show your event times you can do so by turning on the "Always show Day Grid event times" feature in the "Customize" screen. Follow the steps in the image below:
You can see what your events will look like before you turn on "Always show Day Grid event times" and after in the image below:
If you don't see the end times on your events after turning on "Always show Day Grid event times" you'll need to turn "Show end times" on.