No solid numbers here, but I would imagine functional infrastructure would be critical to rebuilding. Trade would suffer serious setbacks with major routes out of commission, especially disconcerting for the Ul'dahn cartels. They probably had ready bodies immediately, but materials may have taken longer to secure and transport (unless they simply conjured all the hewn stone). My guess is planning would have occurred within a month after, construction probably around three months after, completion with magicks and round-the-clock crews nine to twelve months after.
Someone probably has a better idea/source though.
Someone probably has a better idea/source though.