The amazon API works not the same way as eBay API does. The process is slow because of Amazon workflow - when request is sent to Amazon, their servers do not process them immediately as eBay do, but put in a queue. And it may take from 5 minutes to several hours until Amazon processes request and sends response.
Please note, that either you list 2 or 1'000 products - it takes the same time until amazon returns response. So we advise to apply action (i.e. list / stop / revise / relist) to as much as possible products at one time.