SASE3 is the soft X-ray beamline at the European XFEL, and it serves the two instruments "Spectroscopy and Coherent Scattering" and "Small Quantum Systems". A magnetic chicane was installed in the undulator area during summer 2020 in order to enable two-color operation. This magnetic chicane has recently been commissioned and two colors have been produced successfully. To exploit the capabilities of the magnetic chicane and fully control the delay of the two colors, an Optical Delay Line (ODL) will be installed to complement the magnetic chicane. This contribution describes the ODL conceptual design and provides the main mechanical, optical and vacuum specifications and requirements that have to be accomplished.