transferring Aperture library to Photos from External Hard drive

you migrate by opening the Aperture library with Photos -- this may help - Notes on Migrating an Aperture Library from Aperture to Photos for Mac - and these may also - Notes on Migrating an iPhoto Library from iPhoto to Photos for Mac

when you migrate a new Photo migrated library is created on the same drive the Aperture library is on and for Photos it must meet these requirements - and - and you need to make sure the ignore ownership option is checked

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you can not share a volume between a Photos library and TimeMachine - and you certainly would NOT ever want to since you would not have a backup of your Photos library if you did that

Where is it safe to store a Photos Library? Requirements for the external drive

You should not use the drive you are using for Time Machine to host your Photos Library, or Time Machine cannot back up the library. See: Back up the Photos library on Mac - Apple Support

WARNING: If a Photos library is located on an external drive, don’t use Time Machine to store a backup on that external drive. The permissions for your Photos library may conflict with those for the Time Machine backup.

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I get an error message that permissions are incorrect.

This may happen, if the drive with the Aperture Library has been used by Time Machine. Is the drive a Time Machine drive?

This has always been problematic, but since High Sierra it is impossible because Apple changed the way permissions are handled on a Time Machine volume, probably for security reasons.