The time it takes for the listings report to get generated and imported is proportional to your total number of SKUs, both active and inactive. We cannot know exactly how much time per unit of SKUs downloading your listings from Amazon takes since it depends on how busy Amazon servers are when you send your request.
If you find that more time than usual has passed and nothing is happening it means that Amazon did not finish the listings report in time and Seller Engine Plus timed out; the best thing to do at this point is to restart SellerEngine Plus then click Import > Download and Import the last generated listings available on Amazon.
This option will download the last generated listings report. If Amazon finished compiling it but Seller Engine Plus timed out and never imported after your initial request, then you should be able to download your listings much faster.
You can double-check when the latest listings report was generated directly on Seller Central. To do this, go to your seller account, click Inventory > Inventory Reports, and look at the first entry in the list of reports.