Short answer
Ekadashi is the 11th lunar day (tithi) of each fortnight, so it comes twice a month. It is usually kept on the day Ekadashi is running at your local sunrise, and the fast is broken the next morning after sunrise, within Dwadashi (the 12th tithi). The Festivals tool shows this month's Ekadashi days for your city; check the fast-breaking (Parana) window there or in the Panchangam.
How ChiChakra reads this
ChiChakra looks for the day on which Ekadashi prevails at sunrise in your city, using the Sun's centre for sunrise. Some Vaishnava traditions add a stricter test, so when the rules disagree a calendar may list two days, one for Smarta and one for Vaishnava households. Follow the one your family or temple keeps.
Breaking the fast (Parana)
Parana happens on the day after Ekadashi, after local sunrise and before Dwadashi ends. Many calendars also advise waiting until the first quarter of Dwadashi, called Hari Vasara, has passed.
Because Parana hangs on your own sunrise, a time printed for India will not fit Leicester, Toronto or Sydney. Converting an Indian time into your time zone gives the wrong answer; look up your own city instead.
If a full fast is not practical, a lighter one with fruit, milk or a single simple meal is a long-standing option in many families.
Good to know
If you are pregnant, diabetic, on regular medication or recovering from illness, speak to your doctor before fasting; the observance can always be adapted.