It is probably referring to when Christ returns. 7th seal , 7th Vial and 7th Trump. That is about right. 7th trump should be more clear.
Revelation 11:15
King James Version (KJV)
15 And the seventh angel sounded; and there were great voices in heaven, saying,
The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.
The same trump of God mentioned in 1 Thess 4 when Christ returns. And the Same, Last trump Paul teaches about also, in 1 Cor. 15, near the end of that chapter,again when Christ returns when all are changed.
Seven also in Biblical Numerics, there is some meaning behind numbers.
Here is a book that covers this :
PART II
ITS SPIRITUAL SIGNIFICANCE
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SEVEN
We come now to the great number of spiritual perfection. A number which, therefore, occupies so large a place in the works, and especially in the Word of God as being inspired by the Holy Spirit.
In the first part of this book we have enlarged somewhat on the importance of this number in Nature and in Grace, so that we need not here repeat many of the interesting facts already given.
As a number the actual word and number "SEVEN" is used as no other number is. Seven and its compounds occur in multiples of seven in the Old Testament.
Seven occurs 287 times, or 7 x 41.
"Seventh," the fractional part, occurs 98 times, or 7 x 14.
"Seven-fold," occurs 7 times.
The above three numbers together are of course a multiple of seven, but a very remarkable one, 287 + 98 + 7 = 392, and 392 is 72 + 73, or 8 times the square of seven (72x8).
Then again seven, in combination with other numbers, is remarkable, such as fifty and seven, a hundred and seven, etc. There are 112 of these combinations, or 7 x 16.
"Seventy" occurs 56 times, or 7 x 8.
"Seventy," in combination with other numbers, occurs 35 times, or 7 x 5.
It is, however, when we come to consider its significance that the true glories of its spiritual perfection are revealed.
We have just seen that six is the number which is stamped upon all things human, as being emphatically the number of man. Let us first observe the use of the two numbers.