Hi @Aprio
Unmanaged Disks to Managed Data Migration within 1TB can take anywhere from 10-30 minutes depending on the overhead, so long as the operation is successful and not still pending any additional actions, which may take 40 minutes to timeout. Both Disks should migrate in parallel as well, so the time required shouldn't stack.
Keep in mind that this operation does not delete the previous Unmanages Disks, and to prevent additional charges due to these Disks being duplicated, you'll need to delete the old Disks, or Storage Account after verifying the data has been fully migrated, with no faults. https://learn.microsoft.com/en-us/azure/virtual-machines/windows/find-unattached-disks
I hope this helps!