Just did this one and it appears to have been changed. Now there is a blocker in front of it (wagon and junk) and then you can transcribe after you use the azoth staff. Time of day did not appear to matter but it was dark and close to heading into light.
Yep MDRodz was right, I wasnt even able to get this during a daytime train because it had already "been used", but I snuck up here at dawn to get it myself and it spawned the boss. You can run all way up hide in little holes to the side of the elite chest to drop agro at the top of helios. Seems only first person(s) to read it when it spawns can get credit.
I THINK (might have been a glitch) that this only unlocks during the day
I have been finishing lore pages, but had a hard time figuring out how to get this one. Hope my notes help someone! Once you have collected all Brimstone glyphs, go to Helios and get to the top where you can spawn Risen Storm Tefkhonsunut from the tablet behind the three Psychopomps and the elite chest. Call the boss (it has a LONG timer) and THEN you need to read the tablet again to get the lore page while he is "forming." As someone suggested, you can lose aggro by either jumping up behind the stone statue that flanks the elite chest OR the space between the chest and wall next to tablet. If you sneak through that hole and wedge yourself into the corner next to the tablet, you should lose interest from the psychopomps and then activate the tablet. It only spawns once a day I believe.