Based on Dev Trello Card: https://trello.com/c/iaCTwzjW/444-5-rolling-update-should-have-a-tunable-for-the-of-pods-to-bring-up-at-once-deploy I can't see any docs by the devs regarding this and there is a comment by Dan Mace that docs are lacking for this.
Docs PR was here: https://github.com/openshift/openshift-docs/pull/820 Already live in docs: https://docs.openshift.com/enterprise/3.0/dev_guide/deployments.html#rolling-strategy