We also cut down our tree ourselves, and even when it's only been 1 hour, from forest to flat, I always give it a fresh cut, about another cm or so off the base before putting it in water. As soon as the tree is cut, it will start exuding sap which seals off the cut and then it won't be able to take up water.

Also, the way they trim the bark off the ends here to make the trees fit the tree stand prevents the tree from taking up water. The water vessels are only in the layer right under the bark, so if that's shaved off, the tree won't be able to take water.

Our tree from Dec 21 is still super fresh, hasn't dropped a needle yet and still taking up water (though slower now). The Nordmann Tanne is a variety that keeps well.

I had a Christmas tree going for 2 months in Canada once. Finally took it down by Valentine's, but the buds had opened and it was growing fresh needles.