Objection 1. It would seem that the resurrection will not happen suddenly but by degrees. For the resurrection of the dead is foretold (Ezekiel 37:7-8) where it is written: "The bones came together... and I saw and behold the sinews and the flesh came up upon them, and the skin was stretched out over them, but there was no spirit in them." Therefore the restoration of the bodies will precede in time their reunion with the souls, and thus the resurrection will not be sudden.
Objection 2. Further, a thing does not happen suddenly if it require several actions following one another. Now the resurrection requires several actions following one another, namely the gathering of the ashes, the refashioning of the body, the infusion of the soul. Therefore the resurrection will not be sudden.
Objection 3. Further, all sound is measured by time. Now the sound of the trumpet will be the cause of the resurrection, as stated above (Question 76, Article 2). Therefore the resurrection will take time and will not happen suddenly.
Objection 4. Further, no local movement can be sudden as stated in De Sensu et Sensato vii. Now the resurrection requires local movement in the gathering of the ashes. Therefore it will not happen suddenly.
On the contrary, It is written (1 Corinthians 15:51-52): "We shall all indeed rise again... in a moment, in the twinkling of an eye." Therefore the resurrection will be sudden.
Further, infinite power works suddenly. But the Damascene says (De Fide Orth. iv): "Thou shalt believe in the resurrection to be wrought by the power of God," and it is evident that this is infinite. Therefore the resurrection will be sudden.
I answer that, At the resurrection something will be done by the ministry of the angels, and something immediately by the power of God, as stated above (Question 76, Article 3). Accordingly that which is done by the ministry of the angels, will not be instantaneous, if by instant we mean an indivisible point of time, but it will be instantaneous if by instant we mean an imperceptible time. But that which will be done immediately by God's power will happen suddenly, namely at the end of the time wherein the work of the angels will be done, because the higher power brings the lower to perfection.
Reply to Objection 1. Ezechiel spoke, like Moses, to a rough people, and therefore, just as Moses divided the works of the six days into days, in order that the uncultured people might be able to understand, although all things were made together according to Augustine (Gen. ad lit. iv), so Ezechiel expressed the various things that will happen in the resurrection, although they will all happen together in an instant.
Reply to Objection 2. Although these actions follow one another in nature, they are all together in time: because either they are together in the same instant, or one is in the instant that terminates the other.
Objection 3. The same would seem to apply to that sound as to the forms of the sacraments, namely that the sound will produce its effect in its last instant.
Reply to Objection 4. The gathering of the ashes which cannot be without local movement will be done by the ministry of the angels. Hence it will be in time though imperceptible on account of the facility of operation which is competent to the angels.
Source: Summa Theologica (New Advent)