First thing... a fast Travel mechanic is already planned by NQ.
It will function as follows.
As soon as more than one star system will be part of DU after Release (source Roadmaps)
We will get star gates or similar gamemechanic (source press interview)
Travel to another Star System will take about weeks in realtime for the first time to build another gate there (source Q&A)
Because this is an non NDA post, i can only write here whats publically known nor whats already in the game.
The travel times have to be long enough to establish a proper trading mechanic.
In EVE or Elite for example are fast travel mechanics a thing. But traveling although takes long times for a reason.
The trading mechanics need a certain distance between starbases or resource spots with particially long travel times.
In DU as it is an MMO it need min similar travel times to make resource gathering, travelling and tactical PVP worth it.
FTL or instant fast travel will disturb or even destroy those other gamemechanics.
The longer a travel time, the more valuable it will become for all other Game mechanics.
I expect to see extremely long travel times in DU, longer than ever seen in any other game befor.