After 40+ years of working on the same cars I would expect that someone would be able to actually think about how an individual part works and what that actually means for its function, rather than just blindly regurgitate the procedure in the FSM. But?
The UCA's bushings when freshly installed can spin on the UCA camber bolts, the bushing can move up and down with the UCA and spin on the bolt. The UCA bolts are a slip fit into the bushing. The LCA bushings are a press fit. That difference between a slip and press fit determines when the parts have to be torqued.
If the UCA installation is ancient and the car has been sitting and rusting the UCA bushing washers/shells will rust to the bolts and they have to be cut or driven out. But that takes time, and isn't at all true when you first install them. And on the Moog K7103 offset bushings the outer washer is separate from the inner shell anyway, so, the bushing should be able to rotate on the camber bolt indefinitely. Construction matters.
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You can tighten the UCA bolts whenever as long as they're new. Their construction isn't exactly the same as the LCA bushings. Certainly it wouldn't hurt anything to torque them at ride height like the LCA's, but it's not absolutely necessary if everything is fresh. A little common sense goes a long way.
And just like the LCA's, even if you want to torque them at ride height that doesn't mean the suspension has to be loaded and the car fully assembled. You just have to support the suspension at its future ride height, which hopefully is close to the middle of the range of suspension travel if you're using OE style rubber bushings.