After May 8, 2017. For those schools that are participating in Stand-Alone Field Testing (SAFT) on Computers (CBT), the "Welcome to Nextera" emails that provide Nextera Admin login credentials are slated to be sent to District Test Coordinators (DTCs) on Monday, May 8th.
You can find the complete CBT schedule on CBT Support here: https://cbtsupport.nysed.gov/hc/en-us/articles/115000977086-CBT-Timeline-Significant-Events
All schools should be reviewing their test coordinator (District Test Coordinator, DTC, or School Test Coordinator, STC) information in SEDREF. If your school needs to update the test coordinator, then the "school letterhead" process must be followed: https://cbtsupport.nysed.gov/hc/en-us/articles/216061243-How-do-I-change-the-District-Test-Coordinator-DTC-for-my-district-.
(This article is also available in the Nextera Admin FAQ section: https://cbtsupport.nysed.gov/hc/en-us/articles/115001953663.)