Accessing postion of an object x seconds ago in c #

I've gone with the array solution until I can find something better. I tore a few methods out of one of my classes so there may be some small errors here. But you can get a gist of the algorithm I'm using.

     private List<Vector3> _positionBuffer;
     private float _timer = 0;
     private bool _positionBufferFull = false;
     private int _positionBufferStepSize = 0;
     [SerializeFields]
     private GameObject[] _objects;

 private void Start()
 {
 _positionBuffer = new List<Vector3>();
 }  
 
 private void Update()
     {
         //fill the position buffer
         if(_timer < _time)
         {
             _positionBuffer.Add(transform.position);
             _timer += Time.deltaTime;
         }
         else
         {
             if(!_positionBufferFull)
             {
                 _positionBufferFull = true;
                 _positionBufferStepSize = _positionBuffer.Count / (_numCopies+1);
             }
             
             _positionBuffer.Add(transform.position);
             _positionBuffer.RemoveAt(0);
         }
 
     private void PositionObjectsBasedOnTime()
     {
         for (int i = 0; i < _trail.Count; i++)
         {
             int index = (i + 1) * _positionBufferStepSize;
             //Debug.Log(i + " % " + percent + " d " + distance);
             _objects[_trail.Count - i -1].transform.position =_positionBuffer[index];
         }
     }