Inspired by a post in a Mando'a language-discussion server.
Although the base dictionary note has of "which day," perhaps Tion'tuur? means "which part of the day." The base dictionary did not specify hours or minutes, but it does have words for four possible answers: vaar'tuur (morning — from dawn until sunrise), kebii'tra (daytime — after sunrise to the beginning of afternoon twilight), ge'catra (evening — afternoon twilight until sundown), ca'tra (nighttime — from sundown to dawn). A tuur is one planetary day-night cycle (called a "rotation" in Basic). Perhaps there is a veman tuur (true day, or a standardized day based on, say, Manda'yaim) and a yaim'la tuur (local day, or how long a day is on a particular planet). A ca might be portion of a tuur; ca would then encompasses ge'catra and ca'tra. (Or ca might refer to the absence of light from a sun, which is generally during nighttime.)
This could lead to some interesting Galactic sayings about the punctuality of the Mando military:
You won't know when they're coming, but they get the job done when they do.
They might not be precise with time, but Mandos are precise with their strikes.