Travelling Forward In Time & Travelling Backwards Require Entirely Different Technologies
There's an interesting dichotomy between forward and backward; I find it hard to discern which would be easier to traverse. The past already exists and therefore may be easier to 'map' because it's easy to gather telemetry from established events. However, the arrow of time points forward, and thus entropy would naturally carry us forward, via means like time dilation.
So, utilize general relativity to elapse the space around you while keeping yourself in stasis, and you can move forward in time. Exaggerate the variables, and you can control the temporal destination. Easier said than done.
As for backwards movement, let's posit "entropic waves", a fundamental force which can be observed similar to cosmic background radiation. Everything that has or ever will occur leaves a tangible signature, a 'spike' in the fabric of entropy. Observe these spikes, and they become 'grabbable' destinations.
Time dilation can only point you forward. And entropic waves only exist in the past.