A View to Time, inter alia
The Big Picture - Universal Time
Carlo Rovelli presented in his book "The Order of Time" the fundamental idea that universe is consisting solely of processes, also matter is a process, chancing by time. Some processes might be reversible, so that of their point of view it makes no difference witch direction time flows. This are not Carlo's words, but universe itself is also a process, the mother of all processes, chancing by time. Universe is not a reversible process because it has continuously increasing entropy, therefore the time of universe is unidirectional. Particles may have different relative times, but it doesn't affect to universe's aging. GR's far observers time can be regarded as universe's general time, indicated f.e. by CMBR's aging, redshift, and entropy. Beyond cosmological horizon, universal time is flowing normally, we just cannot communicate there because of slow EM media.
Extreme cases - Zero Time
According to GR, in spacetime there exists objects of witch time flow goes to zero compared to far observers time.
The first case are particles at apparent (event) horizon of black holes. These seem to freeze to horizon and their time flow to stop. Their time does not proceed in practice at all, in Planck's time unit of the their proper time the hole universe could advance to the end of it's lifecycle, if particle would stay at horizon that short moment. In this zero time state, events are not finding time to proceed, all chemical and quantum processes would be stopped. And because of wave-particle duality, the matter stops acting as normal matter, and couldn't therefore either be contagious by gravity anymore. Matter's energy would all be transformed into gravity field, as bent spacetime. Therefore this timeless and energyless state is continuing inside horizon, too. The hole inside horizon would be filled by some kind of dead non-vibrating null energy, but information preserving, fluff or fuzz. It could awake to living matter again if touched by positive time, f.e. by the collision of black holes, therefore not allowed to escape.
The second case is light. At light's speed time stops too and traveler at light speed would also seem to froze from outer observer's point of view. But light's inner wave motion does not stop. This could be explained so, that light's energy doesn't go to absolute zero, it's not dead fluff or fuzz as in previous case. Light has a vanishing small mass-energy and therefore it's time flow doesn't go down to absolute zero.
There is also third exceptional phenomenon according to time flow, tangling. Tangled particles seem to be in two distant sites simultaneously, so that the information delivery about it's status is not spending any time at all. In this case, transferred information seems to be completely massless, no energy is transferred. Therefore the delivery speed is faster than light's speed, witch is transmitting mass-energy. GR is ok for massive particles, but real massless information could move faster, actually without spending any time at all.
Neither the uncertainty principle of quantum mechanics nor those phenomenons described above are affecting to the big picture of time, there ain't no evidence of time travel.