Within the planning of your tender it is possible to hide a date or phase from vendors. To do so, navigate to the 'Planning' tab and click the 'Quick Edit' link in the upper right part of your screen.
Using the 'Quick Edit' link allows you to amend the 'Hidden for suppliers' column. For each date / phase, you can select whether or not you want it to be hidden for suppliers or not.
The 'creation date' of the tender is hidden by default.