This code system http://hl7.org/fhir/action-relationship-type defines the following codes:

CodeDisplayDefinition
before-startBefore StartThe action must be performed before the start of the related action
beforeBeforeThe action must be performed before the related action
before-endBefore EndThe action must be performed before the end of the related action
concurrent-with-startConcurrent With StartThe action must be performed concurrent with the start of the related action
concurrentConcurrentThe action must be performed concurrent with the related action
concurrent-with-endConcurrent With EndThe action must be performed concurrent with the end of the related action
after-startAfter StartThe action must be performed after the start of the related action
afterAfterThe action must be performed after the related action
after-endAfter EndThe action must be performed after the end of the related action