The Spring ‘18 release rolled out into Sandbox instances during January, and will be installed into production orgs in February, with the first instances being upgraded on the 3rd Feb.
Sandboxes are continually being patched and at the time of writing we’re running our daily tests against Patch 6.4.
Throughout the Spring ‘18 release cycles we have been monitoring and testing against multiple org shapes. To date, there have been no MobileCaddy related issues seen during the cycle.
Timings for Spring ‘18 can be seen in this graphic, released by Salesforce.
From time-to-time, Salesforce undertakes a maintenance operation called an Instance Refresh. This is performed for various reason, but primarily to maintain good performance. As part of this your org may be moved to a new data center. More information on this, and steps that might be needed, can be found in this Salesforce Help Document.
* Correct at time of writing.
There are currently no Instance Refreshes publicised.