if you want to release the public IP every hour you may need set the IP allocation method as dynamic and click on the IP resource from portal then you need to use the disassociate button and associate it again. once you disassociate the IP the existing IP is gone and you get a new IP address when you associate it. you can also stop deallocate the VM and start it back from portal it will also assign a new IP address every time when the allocation method is set dynamic. This is a manual activity however, you can write PS scripts to do this activity to associate and disassociate as i understand start stop may not be feasible every time
You can see the Public IP pricing here--> https://azure.microsoft.com/en-in/pricing/details/ip-addresses/