Please see below setting within Meraki hub - Site to Site VPN Settings...
Connections to remote peers are arranged by the Meraki cloud.
QUESTION: When the Meraki cloud automation erects this VPN to other Meraki devices, does this VPN timeout after an allotted time, or does this tunnel remain up indefinitely? (on non Meraki devices a time limit is set)
On the Meraki side the tunnel will essentially stay up permanently, but as @PhilipDAth points out, the associations in an upstream firewall or other NAT may well expire. Going for nailed up manual NAT traversal at the Hub end would be a really good idea.