time=distance/speed dont work, i.e object never reach the destination on estimated time.

Unity Engine
1

I was trying to create a code in unity.My aim was to move an object from current position on x-axis(y=0,z=0) to another point on x-axis(y=0 ,z=0).
The object was at (0,0,0) and i was trying to move it at (5,0,0).
With speed=2 the object should reach there in 2.5 seconds(i was using time.deltatime in code).
But it always take 2.48s if i use Vector.Lerp in code(1st code below).When i use movetoward in my another code exactly same happen(2nd code below).When i use distance remaining as a condition in if statement exactly same happen.(4th code below).Always 2.48 seconds instead of 2.50 seconds.
When i use journeytime as a condition in if statement in my third code, the object reach slightly far or near than 5units , for ex - 5.0125 etc.(3rd code below).

1.My lerp code

using UnityEngine;

public class movement1DLerp : MonoBehaviour {
    private Vector3 startPosition;
    public Transform transformTarget;
    public float speed,journeyTime, journeyPercentage;

    void Start () {
        startPosition = transform.position;
        journeyTime = Vector3.Distance(transformTarget.position,startPosition)/speed;
    }

    void Update () {
        journeyPercentage += Time.deltaTime/journeyTime;
        transform.position = Vector3.Lerp(startPosition,transformTarget.position,journeyPercentage);
        if (transform.position== transformTarget.position)
        {
            Debug.Log(Time.fixedTime);
        }
    }
}


2.Movetoward code

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class movement1DMoveAround : MonoBehaviour {
    public Transform TargetTransform;
    public float speed,step;

    //debuginfos
    public float starttime,timelength,estimatedEndtime;
    void Start() {
        starttime = Time.time;
        timelength = (TargetTransform.position.x-transform.position.x)/speed;
        estimatedEndtime = starttime + timelength;
    }

    void Update () {
        step = speed * Time.deltaTime;
        transform.position=Vector3.MoveTowards(transform.position, TargetTransform.position, step);
        if (transform.position == TargetTransform.position)
        {
            Debug.Log("Actual end time = " + Time.fixedTime);
        }
    }
}


3.MY journeytime as a condition in if statement CODE

using UnityEngine;

public class movement1DByTime : MonoBehaviour {

    public Transform targetTransform; //transform of object placed at target position
    public float speed,velocity,displacement,startTime,journeyTimeLength,stopTime,step;

    private Vector3 NewPos;

    void Start () {
        displacement = targetTransform.position.x- transform.position.x ; //distance to be travelled
        if (displacement < 0)
            velocity = -speed;
        else
            velocity = speed;
        startTime = Time.time; //time at beginning of execution of this code
        journeyTimeLength = displacement / velocity; //total time to be taken by journey
        stopTime = startTime + journeyTimeLength; //time at end of journey
        NewPos = targetTransform.position;
    }
    // Update is called once per frame
    void Update () {
        if (Time.time<=stopTime)
        {
            NewPos.x = transform.position.x + velocity * Time.deltaTime;
            transform.position = NewPos;
        }
    }
}


4.distance as a condition in if statement

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class _1DimMultiDirGo2PointOri : MonoBehaviour {

    public int targetPos; //where object has to travel to
    public float speed,step;
    private float distance;
    private Vector2 newPos;

    void Update()
    {
        distance = targetPos - transform.position.x; //distance between current position and target position
        step = speed * Time.deltaTime;
        if (distance >= -step && distance <= step)
        { //A trap to stop potential oscillation if step will be beyond target
            newPos.x = transform.position.x + distance;
            transform.position = newPos;
        }
        else if (distance > 0)
        { //if target is ahead of current position
            newPos.x = transform.position.x + step;
            transform.position = newPos;
        }
        else if (distance < 0)
        { //if target is behind current position
            newPos.x = transform.position.x - step;
            transform.position = newPos;
        }

        if (transform.position.x == targetPos)
            Debug.Log(Time.fixedTime);
    }
}

2

This is due to the fact that update is called directly after start. This means that at time 0 your object has already moved.
Just switch the movement to add the distance afterwards:

using UnityEngine;
public class movement1DLerp : MonoBehaviour {
    private Vector3 startPosition;
    public Transform transformTarget;
    public float speed,journeyTime, journeyPercentage;
    void Start () {
        startPosition = transform.position;
        journeyTime = Vector3.Distance(transformTarget.position,startPosition)/speed;
    }
    void Update () {
       transform.position = Vector3.Lerp(startPosition,transformTarget.position,journeyPercentage);
        if (transform.position== transformTarget.position)
        {
            Debug.Log(Time.fixedTime);
        }
        journeyPercentage += Time.deltaTime/journeyTime;
    }
}