It will arrive in a sudden moment of time but it's speaking of one's fate. Noah was shut up in the Ark by God Himself, then the rain started, and at that very moment the fate of the world was at hand, yet all they saw was rain for the first few days, not the flood. Te Rapture will e just like the days of Noah, they will be driving, eating, giving in marriage, then the floods (70th week) will come upon the world. When that Rapture happens, the fate of all men on this earth are sealed (unless you die naturally before the middle of the week) they will all go through the tribulation period.
The Seals are all opened during the 70th week, we can see that in Rev. 4:1, it says that all of these things are the "HEREAFTER".
And by the way, I agree Rev. 1:1 does indeed mean QUICKNESS or in HASTE, not Shortly (or at least how shortly is perceived nowadays) we can see that the KJV bible translated two Greek words as SHORTLY.
The Reuelation 602 of Iesus 2424 Christ, 5547 which 3739 God 2316 gaue 1325 z5656 vnto him, 846 to shewe 1166 z5658 vnto his y846 x848 seruants 1401 things which 3739 must 1163 z5748 shortly 1722 5034 come to passe; 1096 z5635 and 2532 he sent 649 z5660 and signified 4591 z5656 [it] by 1223 his y846 x848 Angel 32 vnto his y846 x848 seruant 1401 Iohn, 2491
1722 = EN
#1722 ἐν en {en}
a primary preposition denoting (fixed) position (in place, time, or state)
5034 = TACHOS
#5034 τάχος tachos {takh'-os}
from the same as G5036; TDNT - n/a; n n
—Greek Word Study (Transliteration-Pronunciation Etymology & Grammar)
1) quickness, speed
—Thayer's (New Testament Greek-English Lexicon)
From the same as G5036; a brief space (of time), that is, (with G1722 prefixed) in haste:— + quickly, + shortly, + speedily.
—Strong's (Greek Dictionary of the New Testament)
So, the Greek ord TACHOS is where the English word Tachometer comes from whiich of course measures speed. The Gree word EN is speaking about a FIXED POINT [in time in this case).
So, basically, Jesus is just stating the obvious, at a (EN) FIXED POINT IN TIME (Jesus knows that the day nor the hour) I will (TACHOS) come in HASTE or come SPEEDILY. It never meant shortly, of course, the old English word here means in a SHORT TIME PERIOD or in a flash so to speak, Jesus can be there almost as soon as the order is given because He is God after all.
So, we agree that means SPEEDILY. Or in QUICKNESS.
The Birth Pangs however only birth the baby, they are not a part of the 70th week. The 70th week = THE BABY, you cant have Birth Pangs once the baby is delivered.