Ryan Zimmerman and Jason Heyward have a moment at first base. (John McDonnell/The Washington Post)

CHICAGO — The Nationals knew one thing for certain after their 2-1 loss to the Cubs on Monday evening. They must win Game 4 on Tuesday to keep their season alive. The question when they left Wrigley Field on Monday, however, was on exactly when they would play. About an hour after they cleared the visitors’ clubhouse, the league officially announced that the game will begin at 5:38 p.m. Eastern.

The announcement spared them a night of waiting. Originally, the plan depended on the Dodgers and Diamondbacks.

If the other National League Division Series required a Game 4, that game would be the late game Tuesday, catering to the Dodgers’ and Diamondbacks’ West Coast markets. Then the Nationals would have played at 5:38 p.m.

But if the Dodgers beat the Diamondbacks and the Nationals-Cubs series is the only game on Tuesday’s MLB schedule, the Cubs and Nationals were supposed to meet at 8 p.m. Eastern. Unfortunately, Los Angeles’s game at Arizona did not start until 9 p.m. Central. In other words, the Nationals originally would not know their scheduling fate until midnight or later. Game 4 starter Tanner Roark might have gone to sleep not knowing exactly when he would pitch. Now, he knows.

But the forecast for Tuesday afternoon in Chicago: rain, starting midmorning, picking up later, and not stopping all night. If the game were played at 8 p.m. Eastern, it would almost certainly be rained out. Even in the early time slot, rain might intervene.

In that case, Game 4 would have to be played Wednesday instead. The teams would lose their travel day and likely arrive in Washington late Wednesday night or early Thursday morning ahead of Game 5. That game would be played at 8:08 p.m. Eastern.

Whatever happens, the Nationals now know when they are supposed to play Tuesday. Whether they will be able to do so remains to be seen.

Read more on the Nationals:

Best and worst moments from the Nationals’ 2-1 loss in Game 3

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When did Mike Rizzo become a Cubs fan? In the summer of ’69.