How To Build a Time Machine (aka Build Your Own Time Machine) were wasted because time travel is apparently impossible - at least according to this new theory which suggests that 'now' is defined by the extent of expansion of the universe and new time is only created with that expansion.
Thankfully, we don't need to worry too much. To begin with, the idea the theory presents of 'now' being defined by the state of expansion of the universe seems strangely detached from the fundamental idea in relativity that simultaneity is relative - the author seems to postulate a universal 'now' - which just doesn't exist.
And for that matter, it's a bit late to say that time travel isn't possible, because it is always happening on a small scale - relativity makes it inevitable. Tell the Voyager 1 probe, which has travelled over a second into the future that time travel isn't possible.
So even though the TARDIS or the Back to the Future DeLorean will certainly never work, there's no need to write off time travel.