So yes, Twi has gone nocturnal to fit with her wife’s schedule. I’d imagine Twi is fine with the lower end of the recommended amount of sleep. 6 hours out of the day leaves a fair bit of time to be with her friends and do daytime activities while still being there for her strictly nocturnal wife and son.
Offscreen are the Mane 6, Spike and Starlight, maybe a few others depending on your favorite ideas for the future of the characters. I only care for the tuna.