Site to Site VPN Failover Latency/Delay

If I have a site-to-site VPN tunnel with dual WAN connections at both sites and I lose one of the WAN connections, what is the expected downtime between when the connection goes down and when the traffic is rerouted to the next VPN tunnel? I've seen some systems that are supposedly nearly instantaneous while others like Meraki have a 5 minute delay.

For more details, I'm looking at building a network that would have one main data center and one back up data center with about another 12 remote sites. Each site would have dual WAN connections, and each remote site would connect to both of the data centers, with the two data centers connected to each other as well.