being able to control the exact moment the universe ends doesn't seem like it confers very many advantages.
You sure? Seems rather advantageous if your master plan to bring yourself into the universe involves the universe dying, even if it's just to avoid the element of random chance. Time traveler or not, some of the exposition during the Doc Scratch sequence noted that part of the First Guardian's role was to manipulate the sequence of events in a way that would bring about the end of the universe and the introduction of Lord English into it. Even if he's already here, the plan still has to be carried out properly.
I figured it was, yes, Lord English bringing about the end of the universe via the agency of the First Guardians.
Remember, the biggest part of Homestuck so far is stable time loops. Lord English's summoning is already a foregone conclusion, because the universe
will end the the code
will execute, and he will arrive to feast on the corpse of the universe. The question is
how. I think Sburb is furthering that end and allowing that time loop to remain stable, which is why Rose's gatebreaking is a very significant event. Since she's not playing by the rules anymore, perhaps they can prevent Lord English's summoning from occurring at all.
I think a big part of Lord English's interest in maintaining the timeline is displayed in his
Cairo Overcoat. It probably exists as a warning to him that all is not right in Paradox Space, possibly interfering with his future summoning.