“For as the new heavens and the new earth that I make shall remain before me, says the LORD, so shall your offspring and your name remain. From new moon to new moon, and from Sabbath to Sabbath, all flesh shall come to worship before me, declares the LORD.
Isaiah 66:22-23 ESV

The Sabbath and the New Moons will be observed after Judgment Day and the Resurrection. Signs and seasons will still be important in the New Jerusalem on the New Earth.