According to the current understanding of physics, including the theory of general relativity, time is indeed a relative concept. The theory of general relativity describes how gravity and spacetime are interconnected, and it allows for a flexible understanding of time that depends on the reference frame of an observer.
When we talk about the "initial singularity" or the moment of the Big Bang, we are referring to the earliest known point in the expansion of the universe. However, it's important to note that the concept of time as we understand it breaks down at extremely high densities and energies, such as those present at the Big Bang.
At the singularity, the laws of physics, including our understanding of time, cease to be applicable. The universe is thought to have been in a state of extremely high density and temperature, and our current models cannot accurately describe what happened at that moment. Therefore, it is challenging to make definitive statements about the nature of time before the Big Bang.
Some cosmological models and theories, such as certain formulations of quantum cosmology and the concept of the "arrow of time," propose different possibilities for the nature of time before the Big Bang. However, these ideas are still highly speculative and the subject of ongoing research and debate.
In summary, our current understanding of physics suggests that time is relative and that our concept of time breaks down at the initial singularity of the Big Bang. While the Big Bang marks the earliest known point in the expansion of the universe, the nature of time before that moment remains an area of active scientific investigation.