Hmm... Few comments, if I may:
1. You are using public IPs on both sides of the firewall. Is there a legitimate reason for it?
2. It is generally a bad idea to publish your IPs in a public forum, try to at least to obfuscate part of the addresses.
3. If you are simply creating an Automatic Static NAT for the object to be reachable from outside, it is a pretty routine operation.
So long as you are not choosing a conflicting IP, I will not have any issues making this change during normal operating hours (this is a personal opinion, verify your company change management policy for when alterations to the firewall configurations are permitted). Additionally, verify if your firewall is configured to preserve or rematch connections during policy application. If second, it may drop connections for services not explicitly configured to stay connected.
Regards,
Vladimir