As per GR, what you are asking about is gravitational time dilation.
Gravitational time dilation is a form of time dilation, an actual difference of elapsed time between two events as measured by observers situated at varying distances from a gravitating mass. The higher the gravitational potential (the farther the clock is from the source of gravitation), the faster time passes.
We have experiments that already show small differences between clocks tick rate when the clocks are at different altitudes above Earth.
The clock closer to the surface will seem to tick slower (relatively).
In your case, the clock on the planet that has more stress-energy (contrary to popular belief, it is not mass, but stress-energy, and the difference of stress-energy between two points in space that creates time dilation) the clocks will seem to run slower, compared to the clocks on Earth.
So time will seem to run slower in the high mass (in reality it is high stress-energy) system, and clocks will seem to run faster in the low mass ((in reality it is low stress-energy) system.