The Create Thall feature is meant to change the duration of the spell to 1 minute and remove concentration, but in D&D Beyond the spell added by the feature lists the casting time as 1 minute and the duration as 1 hour with concentration. 

There is no way for the system to add the spell with those changes to an existing spell. It should not override the existing entry because the feature is only "when you choose" and not always.

The only way around this is to create a new spell that has the changes for the feature to add that modified spell but in that case the spell becomes available to take as a regular spell, causing confusion.

So, there's no way to resolve this without causing more issues than it is worth. The player can just keep a mental note it's only for 1 minute - something that is very simple and easy. 

I've done that. It's just a note for the developers, as it may confuse new players who refer to the rules on the spell, rather than in the PHB