For your first question: Yes.
For the second question: By view point of Sunnah, Zakat have to be paid exactly at the end of the financial year of a person.
But please mention that the condition for paying zakat is that your property must be to the extent at the end of the year, and if your property got reduced from the extent, you are not obliged to pay zakat for the current year.
Hope this answer could help you.
If you have bounces from your primary extent property, you have to sum up these two money (bounces+the extent) and pay both zakat at the end of the year.
So in your situation, you can pay your bounces zakat singly at the end of the year and wait for the property to go up to the extent.
For pating after or before the end of the year I have to say that, if you know that at the end of the year you have for example an "A$" extent property, you can pay it before the end of the year. But if your extent property doesn't go up to an"A$" and it stay lower than "A$" The money you have paid will be counted as "Sadiqah". It is not good to pay Zakat after the end of the year because you may die (sorry for saying that), but if you want to do that, when you want to pay you have to calculate your extent property at the end of the last year+your extent property form the beginning of the current day, then pay the Zakat.