Really? I never realized that some Premillennialists have that presupposition! As a Premill, I certainly don't have that presupposition! I thought the Millennium was associated with the Sabbath Day, in accord with the Millennial-Day Theory.
Well, obviously Premills do not make this connection. I personally believe that Christians are immediately made "alive with Christ in heaven" the moment we swear on oath to Christ, making him our Lord. We then are given his Sprit as an eternal possession, which qualifies us to partake of his heavenly gifts.
I don't think, personally, this has anything to do with a future Millennial Reign. Our "reign" today is certainly not what our "future reign" will be. We are just benefiting from Christ today in a way that falls short of what it will be in the consummation of all things.
I see nothing wrong with focusing on a "physical resurrection," as opposed to our being spiritually "raised up with Christ" in the spiritual, metaphorical sense. In fact, the primary importance of the resurrection is "physical."
The Church has been Amillennial for a couple of thousand years. The Premillennial belief was early and late in Christian history. We can believe the same things about being "raised up in Christ" today. What will happen in the future is on the speculative side--we just have to maintain an actual physical hope, as I see it. Otherwise, we only have a metaphorical, symbolic hope, which is not enough for me.
The big difference between Amill and Premill is, I think, about whether God will literally restore the nation Israel in the Millennial Age. Those who don't think so find no necessity for a Millennial Age. There will be neither Israel nor nations. Premill thinks the other way, finding Israel and nations critical in the fulfillment of God's literal promises to Abraham. We have to decide according to our best effort.