Well, "Trading Spaces" sort of fessed up when they had that special a few months ago that covered the filming of the New York City episode. Segments are filmed out of order. Those "impromptu" Paige drop-ins are not all that impromptu, and sometimes they're even re-filmed if there's a glitch, technical or otherwise.
And even though it was not said outright, the whole time limit, times up scenario is so that the production crew has time to film the finished rooms and do the pre-reveal interviews. And there have been some unfinished rooms - projects dropped, painting "adjusted", stuff just thrown into a bin or covered up with some curtains, etc...
It's best not to analyze, and just be entertained.
I like Paige. Not sure if I'll miss her or not.
Now, if you wanna talk about Evan Farmer and Jason Cameron on "While You Were Out", well, that would be a totally different story.