We have Youtrack here in company and we also use Gitlab. They use Youtrack for audition, but developers prefer Gitlab to create issues and add spent time.
Is there a way to sync or import issues from Gitlab, with all data (mainly spent time)?
For now the only way you can do this is to write a small piece of software that will do this on schedule. Both YouTrack and GitLab has REST APIs. YouTrack also provides python scripts to import from different trackers (no gitlab among them, unfortunately) that you can use as example: https://www.jetbrains.com/help/youtrack/standalone/2017.1/Migrating-Data-from-Other-Trackers.html.