After the 144,000 are sealed (Revelation 7), the 7th Seal is broken (Revelation 8:1-2), releasing the 7 Trumpets. This coincides with the start of Daniel's 70th Week, and the start of the ministry of the 2 witnesses, who announce the first 6 Trumpets in advance from the Temple. The 7th Trumpet is at Mid-Tribulation.