According to Revelation, the ‘sign of the dragon’ of Rev 12:3 will take place sometime after the ‘Great Sign of Revelation 12:1-2’, but before the ‘Abomination of Desolation’, which is when the ‘Woman’ is described as fleeing into the wilderness. (We are not told how much time will elapse between these two signs.)
The ‘sign of the dragon’ symbolically alludes to a severe war / invasion / distress in Israel (the ‘Woman in travail’) as well as an incursion of fallen angels, perhaps disguised as aliens, ‘stars’ or something equally disturbing and surprising. This particular incursion of fallen angels, however, is NOT when Satan and ALL his angels will be cast from heaven. That incursion will take place later on the Timeline and immediately precede the ‘Reign of the Beast’.