You are really a great help.

modules: [
...
{
    module: "clock",
    position: "top_left"
},
{
    module: "calendar",
    header: "US Holidays",
    position: "top_left",
    config: {
        calendars: [ {
	    symbol: "calendar-check-o ",
            url: "webcal://www.calendarlabs.com/templates/ical/US-Holidays.ics"
        } ]
    }
},
...
]

You have to put the fetchInterval setting into the config setting section of the calendar module. The result would look like this (just typing the calendar module’s part for simplicity):

{
    module: "calendar",
    header: "US Holidays",
    position: "top_left",
    config: {
        fetchInterval: 1000 * 60 * 1,
        calendars: [ {
	    symbol: "calendar-check-o ",
            url: "webcal://www.calendarlabs.com/templates/ical/US-Holidays.ics"
        } ]
    }
},

The value 60 * 1000 * 1 retrieves the calendar from the source (see parameter url) every minute. Please note that the interval time value is given in milliseconds according to the documentation. When you pick a value make sure that your fetching is not too aggressiv. Too frequent syncs take bandwidth on your network, increases CPU load on Raspberry Pi, and there might be limitation enforced by the calendar provider.

According to the doc “To use this module, add it to the modules array in the config/config.js file”, may I know the module should be added under which section?

Appreciate your guidance.