It is short for "That is you done". It signifies that Madam Malkin has finished putting pins into robe that Harry is wearing. It is a common (UK) English phrasing used to mean that someone has finished the work, or a stage of the work, that they are doing on behalf of another person. Here the pins have been placed to show the wanted length and next someone can sew the robe to that length.
The whole ending of that paragraph is written in a poetic register, violating the rules of grammatical prose and even normal usage. There is no rule against trying to write in a poetic register except that others may find it obscure, pretentious, or both.
The force that through the green fuse drives the flower drives my red blood is meaningless if interpreted literally, but it is great poetry. Of course, few of us can match Dylan Thomas, who wrote the only decent villanelle in the English language, so, in my view, few of us should even try.
The meaning of that purple prose is What was needed -- what Emily needed -- was a woman emancipated from the pretences of tradition, a woman as strong as any father imagined by tradition, a woman willing to scorn the dictates of traditional deference, willing to speak out and to act.
Some can write like Dylan Thomas; most of us cannot. In my opinion, those of us who cannot should learn to write prose. As written, the quoted passage is facially absurd: at what time in the history of the world were women not able to speak. What is meant is that women would be punished, socially or physically, for doing certain things and so, quite rationally, were frequently unwilling to do them. The women who emancipated women were brave women who did what other women could have done but feared to do. I wear my clothes, not men's clothes.
EDIT: The quote about clothes (actually a slight mis-quote) is from the 19th century feminist doctor, Mary Edwards Walker, the only woman to have won the Cobgressional Medal of Honor, which was awarded for her work as a battlefield surgeon during the Civil War. I should have attributed it initially.
Best Answer
"Sufficient" means "enough", "an adequate amount". So "sufficient time" means the amount of time you need to get a certain job or task done. "Given sufficient time" is a fairly common phrase used when you want to say that something may be difficult, but if the person attempting the task is allowed to work on it for long enough they should be able to succeed. Like, "I don't know the answer to that question, but given sufficient time I could look it up." Or, "We can't get that done today, but given sufficient time -- probably about a week -- we could complete that for you."
"Overtime" is a little different. "Overtime" is used in sports to mean that a game is allowed to go beyond the usual time limits, usually because there is a tie score and so we keep playing until one team or the other scores and can be declared the winner. In business, "overtime" means hours worked over your regular hours, usually 40 hours per week. In the U.S., at least, many workers are paid 150% of their normal hourly wages for each hour of overtime.
"In the long run" is a phrase used to distinguish the long-term effect of something from short-term effects. Like, "Dieting and exercise may seem painful now, but in the long run you will be healthier if you keep it up." Or, "In the short term the stock market has many ups and down, but in the long run it always go up." It is often used to express the inevitably of some final outcome, like JK Galbraith's famous retort to criticisms of the long term effects of his ideas: "In the long run, we are all dead."