When does the great war in heaven happen during the tribulation?
The great war in heaven occurs at the midpoint of the tribulation, the final seven years. At that point Satan and his angels fight against Michael and the other angels, are defeated, and are cast out, leaving only three and a half years until Christ returns to set up His kingdom.
Les explains from Revelation chapter 12 that at the midpoint of the tribulation, that final seven years, there is going to be a great war in heaven. Satan and his angels fight against Michael and the other angels, and finally Satan and his angels are defeated and cast out. Then a loud voice in heaven says salvation and strength and the kingdom of our God have come, for the accuser of the brethren is cast down, who accused them before God day and night. Only three and a half years are left until Christ would return and set up His kingdom.