The correct answer is 24 hours.
Imposition is the process of arranging pages on a printing plate so that they will print correctly when the plate is inked and run through a press. It is a critical step in the printing process, as it can affect the quality of the final product.
The amount of time required to impose a line block depends on a number of factors, including the number of pages in the block, the complexity of the layout, and the experience of the person doing the imposition. However, it is generally recommended that imposition be done at least 24 hours in advance of printing. This will allow enough time to make any necessary changes and to ensure that the plate is ready to go when the press is scheduled to run.
Option A, 12 hours, is not enough time to impose a line block. Option B, 24 hours, is the recommended amount of time. Option C, 18 hours, is more time than is typically needed, but it may be necessary in some cases. Option D, 22 hours, is too much time and may not be necessary.
In conclusion, the correct answer is 24 hours.