MonoBehaviour.InvokeRepeating

Description

Invokes the method methodName in time seconds, then repeatedly every repeatRate seconds.

Note : This does not work if you set the time scale to 0.

using UnityEngine;
using System.Collections.Generic;

// Starting in 2 seconds.
// a projectile will be launched every 0.3 seconds

public class ExampleScript : MonoBehaviour
{
    public Rigidbody projectile;

    void Start()
    {
        InvokeRepeating("LaunchProjectile", 2.0f, 0.3f);
    }

    void LaunchProjectile()
    {
        Rigidbody instance = Instantiate(projectile);

        instance.velocity = Random.insideUnitSphere * 5;
    }
}