It's not just completing the data return, it has to actually render all of the pages to determine what M is. Depending on the complexity of the report and whether or not there are subreports, this can cause long delays before the first page is rendered. This is not a process for which there is a "fix" to make it faster - it is what it is and there is nothing to fix.
-Dell
A computer only does what you actually told it to do - not what you thought you told it to do.