About 7500 words over the last week. Only 2500 or so are part of the WiP, but the others are for a novella which is something of a prequel I'm considering for one of Musa's theme calls.
I've had good luck restricting any mental "leg stretching" to the same story-verse. Granted, a four or five thousand year timeline gives me plenty of room, yet everything eventually contributes to the WiP.
The thousand-years-before prequel got a personal rejection from the editors of Clarkesworld & Penumbra, and it's working it's way into becoming a chunk of the novella. So it counts as backstory/worldbuilding. And that, in turn, has generated a couple of characters in the novella who will nicely fill some holes the WiP had in it's cast. I'm thrilled that when I have an Idea Compulsions that would require something of a change in settings, I just need to jump to a different point in the WiP's timeline. And it then creates either seed material, or something to build story towards. I think I've bumbled into a pretty good system.