As a general pattern, "until" implies something happens immediately after a condition occurs, while "before" does not.
Both "Most children do not start school until they are six years old." and "Most children do not start school before they are six years old." have the same technical meaning. You don't see many children of ages three, four, or five in school. However, the connotations are different. "Until" suggests that children tend to start school as soon as possible once they are six, as though "until they are six years old" is the last hurdle in their way. "Before" also suggests that children start school when they are six, but also suggests that some start at seven or eight, or even never go to school at all.
This pattern is, of course, a fuzzy line. However, it is visible in these two stories about a sprinter:
Do not let your feet start moving before the gun fires. Once the gun fires, give it everything you've got.
Do not let your feet start moving until the gun fires, then give it everything you've got.
In the second sentence the word "until" causes the listener to treat "the gun fires" as a trigger, causing action. This lets us construct the rest of the sentence starting with "then." In the first sentence, with before, it is hard to use "then." The speaker is forced to reintroduce the gun in a second sentence. The following phrasing is awkward
Do not let your feet start moving before the gun fires, then give it everything you've got.
It is probably grammatically correct. However, the first half of the sentence leaves the listener dwelling in the region "before the gun fires," and then the listener has to quickly catch up to the moment for "then give it everything you've got." The sentence formed with "until" brings the listener right up to the moment where the gun fires, so their perspective is more correct for making sense of "give it everything you've got."
The manual holds that women mustn't choose a programme themselves, but instead wait to be assigned to a module.
You use a comma before "but" if it introduces an independent complete clause.
As there's no independent clause after "but" in the sentence presented above, it doesn't need a comma before "but".
Best Answer
You normally use the until-clause after the main clause. When you do so, you don't use a comma between the main clause and the until-clause.