Page 554 — Seventh Sense
It's natural, when the party is split, for the rest of the players to want to come running when trouble's going down. Even if there's no way for them to know.
Personally, I tend to be lenient about it when it can be finagled, since the alternative is players being left out of the action more often than not. But when I want to raise the stakes, I reserve the right to say, "No, you don't magically show up in time. This is happening now."
Transcript:DM: Your prank is over, but Nightmare Night is not. Thanks to the kids getting on board with Luna’s involvement, the festival returns to its former life. The adult ponies dance, play, mingle, and shop, while the foals continue their search for more candy – some for themselves, and some to “tribute” to “Nightmare Moon.”
Princess Luna: Oh dear. Now I need to find a use for all these sweets… I have not quite thought this through…
Rainbow Dash: <roll>
DM: And you miss.
Rainbow Dash: What?! He’s a thief! How can he be an AC tank?!
DM: You haven’t rolled THAT high…
Rainbow Dash: Hey, uh, this would be a great time for one of you to randomly wonder where Rainbow Dash is… Just sayin’.
Applejack: <gasp!> But Rainbow! … That would be metagaming.
Rainbow Dash: …Rrrrrgh. Hate. All the hate.