This varies wildly. Sometimes, you may just get a response e-mail in a day or three saying thanks, and that we've fixed the typo. This is normal when you've just reported one or a few obvious typos.
Where there is some text missing, or the changes you suggest are otherwise not obvious, we may have to find someone with an eligible copy of the book to confirm the changes, and that might take time. Normally, you will get an e-mail explaining that within a week.
Sometimes, even though you've noticed only one or two small typos, one of the Posting Team who was looking at it may find many more, and decide that the whole text needs to be re-proofed. This may also take time.
If the text needs a lot of changes, we may post a new EDITION [R.35] of it, with a new filename: e.g. abcde10.txt may become abcde11.txt. In this case, you will receive a copy of the e-mail sent to the posted list announcing the new file. Our current rule of thumb is that we create a new edition when we make twelve significant changes, but we judge each on a case-by-case basis, and especially will usually not make a new edition if the original was posted recently.