From Cloud 1.2.18 version and Server/DC 2.5.9 version TeamBoard TimePlanner supports mapping Start date and End date to Jira fields. Each project in Jira has different Screen Scheme with different Fields therefore you need to configure the field mapping at project scope.
From Jira go to Apps → TeamBoard TimePlanner → Settings → Date Fields
Select the project you want to configure in the dropdown list, then the same configuration with project board settings appears and you can map the fields.
Depend on your project Screen Scheme the issue types in project may not have the fields you picked, this list shows a current statuses. The issue types which don’t have the fields won’t work properly, you should add the fields to the Screen of those issue types
After configuring correctly, issues in the project will use Jira fields when planning with TimePlanner