The common rule in doing an import is to allow up to 24 hrs for the import to be completed regardless of the size of the import. If it doesn't complete within a day then Chat With Support and reference this article.  

If you have an import that has been waiting to be processed for over 24 hrs please provide the name of the batch and we will take a look. If there is a deadline, please submit the import days ahead to make sure they are completed on time.

Please note: We have noticed that imports are running faster on Tuesdays, Wednesdays, and Thursdays because they are not as busy. In addition, doing imports at night are more successful than other times.