Each Raid Orb will replenish or regenerate for exactly one (1) hour. That is a total of three (3) hours if you have used all of your orbs.
To be able to maximize your Raid runs, we advise that you do take note of the time you completely use your orbs so you can re-do it again the moment it fills up.
If you can not wait for the Raid Orbs to replenish on their own, there is always an option to use Gems.
We highly recommend working up a schedule on what to do next whenever waiting for Raid Orbs. A good example of this is alternating between Arena and Raid Battle in order to start the refresh timer on both contents. Once finished with both Arena and Raid Battle you can solely focus on other quests and wait until either orb have been replenished.