Why should they pray that their flight not be in the winter?
They should pray their flight not be in winter because the weather can then be adverse and miserable, as Jesus instructed. The same prayer also asks that it not be on the Sabbath, since Israel will be going back under the law.
Les explains that Jesus told them to pray their flight not be in the winter, because the weather can be adverse and miserable. He also said to pray it not be on the Sabbath day, since Israel is going back under the law; if they have the temple, they naturally will return to the law. Les notes that a law before the Jerusalem Knesset has been proposed for several months to reestablish the Sabbath in every category of Israel, and there is much controversy.
But pray ye that your flight be not in the winter, neither on the sabbath day: