The winning designer signs the Copyright Transfer Agreement as soon as they enter the design handover phase. First they sign the Copyright Transfer Agreement and then they upload all the required source files for the contest holder.
Note: Design Transfer Agreement once signed, transfers the ownership of the winning designs. Between signing the agreement and releasing the prize payment, the Contest Holder will still be able to request small tweaks to the final design if required. You will get a 14-days timeline for revisions and modifications.