The concept of negative mass is purely speculative and hypothetical at this point. It has not been observed or confirmed to exist in the universe. The current understanding of physics is based on the existence of positive mass, which is the mass associated with normal matter.
In general relativity, the presence of mass, energy, or stress distorts the fabric of space-time, resulting in the curvature of space and the effects such as time dilation. However, the behavior of negative mass is not well understood, and it would require a significantly different set of physical principles and equations to describe its effects accurately.
If negative mass were to exist and could somehow be manipulated or interacted with, it is not possible to definitively predict its effects on time dilation or the possibility of time travel. Speculating about the behavior of negative mass is highly speculative and goes beyond the current scientific knowledge and understanding.
It's worth noting that time travel and the manipulation of time are subjects of ongoing scientific inquiry and exploration, but they are highly complex and still in the realm of theoretical possibilities. Any discussion of time travel or its potential mechanisms involves many unresolved questions and theoretical challenges.