Azure HA Cluster deployment

Hi Folks, I am in process of designing a DMZ in Azure with Load balances and Firewalls. My question is: if i deploy a HA cluster that receives traffic from internet and forwards it to firewall without Nating, 1) how much time will it take to fail over from active to standby? Reason i am asking this question is that i understand there are a few API calls that are need to be made in AZURE as it does not support gratuitous arp. 2) Will it be possible to configure multiple Public IP's on the external interface of F5 cluster to differentiate the traffic for different services?