The holy period of Ramadan begins on Wednesday and will last a month for those who observe it. During Ramadan, people fast from dawn to sunset. Referee bodies for the Premier League and English Football League issued guidance that any games which take place during sunset should be paused to allow players to break their fasts. They are encouraged to make a note if there are any players who are observing Ramadan so they can make that decision. The clubs will likely supply the referees with that information.
Referees will choose a good moment to pause the game so that players can get liquids, energy packets, supplements, etc.
Among these players will be Mohamed Salah. Liverpool’s games against Chelsea and Leeds United begin at 8PM BST, so they should not be affected. The Arsenal game starts at 4:30PM BST, and so this may come into play then, should Salah be on the pitch at that time.
The guidance says that referees should use their best judgment — never a good idea — for how long the break should last. Presumably it will be similar to hydration breaks during summer matches.