Imagine fasting here!

Don’t worry, the shari’ah has it covered:

قلنا‏:‏ يا رسول الله وما لبثه في الأرض‏؟‏ قال‏:‏ ‏”‏أربعون يوماً‏:‏ يوم كسنة، ويوم كشهر، ويوم كجمعة، وسائر أيامه كأيامكم‏”‏ قلنا ‏:‏ يا رسول الله ، فذلك اليوم الذي كسنة أتكفينا فيه صلاة يوم‏؟‏ قال‏:‏ “لا، اقدروا له قدره”

We asked: “O Messenger of Allah! How long will he [the dajjal] stay on the earth?” He said, “For forty days. One day will be like a year, one day like a month, one day like a week and the rest of the days will be like your days.” We said: “O Messenger of Allah! Will one day’s Salat (prayer) suffice for the Salat of that day which will be equal to one year?” Thereupon he said, “No, but you must make an estimate of time and then offer Salat.”