One point in the contrail argument's favor that is overlooked on this thread quite a lot is that no one is claiming that the plane that supposedly created it was headed into LAX, but that it was headed to Phoenix en route from Hawaii, so it would be at very high altitude.
I agree that the picture doesn't indicate a vertical path and could easily be of something at very high altitude coming over the horizon. But the "vertical" (or not) aspect is not what makes me think it was or wasn't a missile. Instead, it's the shape and density of the plume, the corkscrewing, the single-source, and the testimony of the guy who took the video who said (and I paraphrase) that it disappered UPWARD into the sky, not off in the distant horizon. Planes making contrails disappear in the distance; missiles launching things disappear into the sky. There's a difference, and it sounded to me like the latter is what the cameraman said what happened.
As for your question I put into italics on seeing the exact same thing a day or two before: Living near the coast within sight of Vandenberg launches for virtually half a century, and having an interest in watching the airborne activity out of Vandenberg (watching with binocs, where the burn and separation stages are clearly visible and spectacular), it has been my repeated experience that I'd see the same thing about the same time every night for sometimes several days in a row, or the same time every other day for a week, or in some scheduled pattern -- they weren't always just one-offs. So it is no stretch for me to think this kind of test (I hope that's what it was) was repeated night to night, because of what I've witnessed with my own "lyin' eyes" over the course of the years.
It's not going to disappear over the horizon because it's approaching you from the west and still hundreds of miles away, near sunset.
The screenshots I've seen made from the video seem to show that it never went more than a couple degrees above the horizon while he was recording. It just looks like it's going higher in the sky when he's zooming in.
From the cameraman's perspective it's rising upward into the sky. In reality, it's simply following the curve of the earth. As it does, it goes from being below the horizon to being above the horizon, and if he would have watched long enough it would have shown itself to be an airplane flying past on it's way to Arizona, or wherever it was going.