A.T. Robertson Commentary Matthew 24:20

"And pray ye that your flight be not in the winter, neither on a sabbath:" — Matthew 24:20 (ASV)

In winter nor on a sabbath (χειμωνος, genitive of time, μηδε σαββατω, locative of time). In winter because of the rough weather. On a sabbath because some would hesitate to make such a journey on the sabbath. Josephus in his Wars gives the best illustration of the horrors foretold by Jesus in verse 21.