If you haven't read the post on the Business Central for Partners blog about "Scheduling your April 2019 Upgrade for Business Central", I recommend reading it thoroughly.
https://community.dynamics.com/business/b/businesscentraldevitpro/archive/2019/03/27/scheduling-your-spring-2019-upgrade-for-business-central
It has several very valuable points about enhancements to the Business Central version upgrade process.
Some of the key points are:
Beginning with the April '19 release, we will also send notifications for preview version availability, upgrade scheduling, extension validation, and upgrade failures.