1. Is the delegate access of UserA given to UserB will not be migrated for UserB unless if we are migrating the UserA OneDrive?
Scenario based, but Make sure that the owner onedrive is migrated before the shared users is migrating to have the shared permission is available, else the shared access will be skipped for migration for the shared user.
2. How long shall a Migration OneDrive can be initiate after Provision?
Recommended best practice is to have at least 24 hours before a MIgration can be happen. Please reach to our Best Practice Document
here. "
On Demand Migration Strategy and Best Practices for Migrating Active Directory, Mail, OneDrive, SharePoint Online, and Teams Content"