I think you are making two or more mistakes here, at once so it will not help you as much if I try and fix your code.
To get created and modified dates from a different tiddler you need to name that tiddler.
{{tiddlername!!fieldname}}
This is the transclude short cut if you are happy to hard code the title and fieldname.
- In a filter you would use
[{tiddlername!!fieldname}]
But we can also write this in a filter [[tiddlername]get[fieldname]] which has the advantage we can instead use variables such as [<target-tiddlername>get<target-fieldname>] or from local fieldnames [{!!target-tiddlername}get{!!target-fieldname}]
See how you go and feel free to ask follow-up questions.
Eg;
[{!!select}get[modified]format:date[TIMESTAMP]]