Once you have created a new Tender and you want to copy the planning from a previous Tender, you can easily use templates.

Go to the original Tender you want to copy the planning from (you have to be a participant in this tender). Under the third tab 'Planning' you'll find a 'Save as Template' link at the top right part of your screen.

Name and save the template planning.

Now navigate to the tender, where you want to use the existing planning. Go to the third tab again: 'Planning' and now choose 'Import template' to load the existing planning into your new tender.

Using this option events are added to the planning and all dates and times are re-used relative to the start date of this new tender.

I cannot select the template I've just created? 
If you are not able to re-use the planning, most probably both tenders have a different procedure with possible additional phase(s).
Look in the original tender what procedure was used under: Tender Properties > Procedure, and make sure your target tender has the same procedure assigned to itThis is a prerequisite for importing a Planning template.

Delete a planning template

Open a tender in preparation, go to Planning. Click on Import template and select the template you want to delete. Click on the trash bin icon to delete the template.