Edit: Just to clarify, the time-variant system exception does not apply in this case. It really is an entropy thing, moreso than an energy thing (which is constant in every particle decay that happens on Earth.)
https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
Just need to find a tie-in to 5G and I can write my own time-cube parody website.
(The article is also very interesting, of course!)
Conservation laws (Noether's theorem) are dependent on the way the physics is voiced, mathematically. Saying "energy is conserved" is the moral equivalent of looking at Newton's laws and just ignoring GR. GR tells us new, precise, and amazing things about conservation laws. It's just that, unfortunately, they're a little hard to translate into English.
If you're not expecting the spacetime background to be changing rapidly during your experiment, it's pretty moral to say energy is conserved.