As far as I have been able to find out, according to Baptists, the names of the Elect were written in the Book of Life “from the foundation of the world.” This is because Baptists believe in God’s sovereign right to predestine some to salvation. Below are extracts from sermons by Charles Spurgeon, one of the foremost of Baptist preachers:
A sermon by C. H. Spurgeon 1876: “Notwithstanding in this do not rejoice, that the spirits are subject to you; but rather rejoice because your names are written in heaven.” Luke 10:20:
This joy consists in knowing our election; “knowing, dearly beloved, your election of God,” knowing that your names were written in heaven from before the foundation of the world.
To be written in heaven means that you claim the right of citizenship in the New Jerusalem, “the church of the firstborn, whose names are written in heaven.” Just as there is a roll kept by great cities in which they inscribe the names of citizens, so we rejoice that our names are written in the roll of the city above, and that henceforth our citizenship is in heaven, from where we look for the Saviour, the Lord Jesus. This is a broad subject for rejoicing, for it includes priceless privileges and honours more than royal.
We also rejoice that our names are written, that is, known and published in heaven. Paul mentioned certain of his fellow servants of whom he said, “whose names are written in heaven”: as much as to say though they have neither fame nor honour here they have a perpetual record where honour is worth receiving, namely, before the throne of God. The heavenly writing indicates that we are part and parcel of Christ’s new kingdom, we are inscribed among his soldiers, we are commissioned to bear hardness for his sake. We are written in heaven among the friends of Jesus, we are considered members of the sacred brotherhood. In the great book of the divine Fatherhood, we are numbered among the children, and henceforth we shall be regarded and treated as belonging to the one family in heaven and in earth. This is the matter concerning which we are called to rejoice. “Rejoice that your names are written in heaven.”
“He who overcomes, the same shall be clothed in white raiment; and I will not blot out his name from the book of life, but I will confess his name before my Father, and before his angels.” There stands your name still recorded in the Lamb’s book of life, though many a tear of yours might well fall upon it to think what grace it is which keeps it there and will keep it there for ever.
If you are forgiven, your name is written among the forgiven. If you are indeed quickened and made alive, your name is written among the living in Zion... The Lord does not give to any soul dead in sin the least right to believe that it is written among the living, neither does he give to any ungodly man the liberty to hope that he is written among the elect of God. We must have evidence, not dreams and airy suppositions; and the evidence of being written in heaven is that a man has been called by grace out of the world to follow Jesus. We see our election by our calling, and not in any other way. We may know what is written about us in heaven by what is written within us on earth. If grace has written upon your heart until you are “an epistle of Christ, known and read by all men,” your name is in his secret book. If you are trusting in the Lord Jesus Christ you are his, and the Lord knows those who are his, and has written them down in his own private tablets which he carries near his heart. If your name is among true believers on earth it is among the redeemed in heaven: you need not question that, for the declarations of Scripture put it beyond a doubt.
Other sources provided these insights:
17th Article Predestination and Election: "Predestination to life is the everlasting purpose of God, whereby (before the foundations of the world were laid) he hast continually decreed by his counsel secret to us, to deliver from curse and damnation those whom he hath chosen in Christ out of mankind, and to bring them by Christ to everlasting salvation, as vessels made to honour. Wherefore they which be endued with so excellent a benefit of God be called according to God's purpose by his Spirit working in due season: they through grace obey the calling: they be justified freely: they be made sons of God by adoption: they be made like the image of his only-begotten Son Jesus Christ: they walk religiously in good works, and at length, by God's mercy, they attain to everlasting felicity."
Waldensian Articles of Faith: "That God saves from corruption and damnation those whom he has chosen from the foundations of the world, not for any disposition, faith, or holiness that he foresaw in them, but of his mere mercy in Christ Jesus his Son, passing by all the rest according to the irreprehensible reason of his own free-will and justice."
The Baptist Confession of Faith (1689)- 3rd Article: "By the decree of God, for the manifestation of his glory, some men and angels are predestinated, or foreordained to eternal life through Jesus Christ to the praise of his glorious grace; others being left to act in their sin to their just condemnation, to the praise of his glorious justice. These angels and men thus predestinated and foreordained, are particularly and unchangeably designed, and their number so certain and definite, that it cannot be either increased or diminished. Those of mankind that are predestinated to life, God, before the foundation of the world was laid, according to his eternal and immutable purpose, and the secret counsel and good pleasure of his will, hath chosen in Christ unto everlasting glory out of his mere free grace and love, without any other thing in the creature as a condition or cause moving him thereunto."
The Baptist Confession of Faith (1689): http://www.romans45.org/creeds/bcof.htm
My only comment about the expression "before the foundation of the world" is that I take this to mean before God created Adam and Eve and placed them in the Garden of Eden.