Unity how to set Off mesh link speed

You can have an Update or FixedUpdate function check when the agent is on an off-mesh link, and modify its speed in response, as shown here:

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

public class LinkSpeedScript : MonoBehaviour
{

    public NavMeshAgent agent;
    public bool linking;
    public float origSpeed;

    // just change linkspeed to alter off mesh link traverse speed;
    public float linkSpeed;

    void Start()
    {
        origSpeed = agent.speed;
        linking = false;        
    }

    void FixedUpdate()
    {
        if (agent.isOnOffMeshLink && linking == false)
        {
            linking = true;
            agent.speed = agent.speed * linkSpeed;
        }
        else if (agent.isOnNavMesh && linking == true)
        {
            linking = false;
            agent.velocity = Vector3.zero;
            agent.speed = origSpeed;
        }
    }
}

This seems to work with my NavMeshAgent settings.

This unity forum post suggests handling the traversing yourself.

if(agent.isOnOffMeshLink && !MoveAcrossNavMeshesStarted){
    StartCoRoutine(MoveAcrossNavMeshLink());
    MoveAcrossNavMeshesStarted=true;
}

IEnumerator MoveAcrossNavMeshLink()
{
        OffMeshLinkData data = agent.currentOffMeshLinkData;
        agent.updateRotation = false;

        Vector3 startPos = agent.transform.position;
        Vector3 endPos = data.endPos + Vector3.up * agent.baseOffset;
        float duration = (endPos-startPos).magnitude/agent.Velocity.magnitude;
        float t = 0.0f;
        float tStep = 1.0f/duration;
        while(t<1.0f){
            transform.position = Vector3.Lerp(startPos,endPos,t);
            agent.destination = transform.position;
            t+=tStep*Time.deltaTime;
            yield return null;
        }
        transform.position = endPos;
        agent.updateRotation = true;
        agent.CompleteOffMeshLink();
        MoveAcrossNavMeshesStarted= false;

}

To make it look like a jump, you could

1. lerp between the two positions and play a jump animation on a child node of the hierarchy
2. calculate the y-position yourself, e.g.
   s = 0,5 · a · t2 + vo · t + s0
   with vo being the initial velocity and s0 being the inital position. Use this formula for y.