Here's how I think time works. Our perception of time is based solely on energy and the rate at which it can be transferred. Taken at its most basic unit, it is the transfer of 1 unit of energy across a distance of 1 Planck Length. The velocity is constant at the speed of light. All matter comprises energy. E=mc2 states that all mass is comprised solely of energy. Every particle/atom/molecule that we are made of, is solely comprised of energy. These components each have a cycle, for example, the orbit of an electron. Due to the similar position we have within our gravity well, all our component parts will have roughly the same cycles, hence we measure time at roughly the same rate. If we were to position ourselves in a gravity well with an increased gravitational force, all of our mass would under go compression. Not only is our mass compressed but also space, and with it the space that the electron has to travel in its orbit. A Planck Length, relative to here on earth, is now reduced. Basically, the electron would have more space to traverse to complete a single orbit and because the rate that energy is transferred is a constant, it will take a longer period of time. If the firing of a neuron in our brain is dependant on the chemical properties, more specifically the orbit of an electron, then it will fire at a reduced rate. Everything would appear normal to us, based on the rate at which our brains work, but we would be experiencing time dilation. Taken into a lower gravitational force and space under goes decompression, resulting in faster energy cycles. With velocity, you are adding energy to the particles/atoms to move them. This energy is being added into the already existing cycles resulting in a longer period of time for each cycle to complete as there is now more energy to be transferred. Whether you increase the amount of space involved (GR) or increase the amount of energy involved (SR) the result is the same, you change the energy cycles and subsequently time.