Hello!

I'm trying to write a query to filter based on a 'duration', i.e., something like
`date1 < date2  + 20 days`

As far as I know, I should be able to use either `xsd:duration` or `xsd:dayTimeDuration`, but using either throws an error related to a missing column name.

For instance, this query: 

```
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT ?test
WHERE {
    ?a ?b ?c
    BIND ("PT120M"^^xsd:duration as ?test)
}
LIMIT 1
```
Throws a `Virtuoso S0022 Error SQ200: No column PT120MD.`
Same with basically any example from [xsd:dayTimeDuration](http://www.datypic.com/sc/xsd/t-xsd_dayTimeDuration.html)

Am I missing something on the syntax? (It does seems to work on the paid version).

I can manage by using either a direct addition (`dateTime` + a number of seconds), or `bif:dateadd`, but I'd rather not use an engine-specific solution if I can avoid it.

(I tested by directly building from the current main branch, and by using a docker image based on 7.2.9)
Behaviour of `xsd:duration` and `xsd:dayTimeDuration`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Behaviour of `xsd:duration` and `xsd:dayTimeDuration`
Issue date:

--- start body ---
Hello!

I'm trying to write a query to filter based on a 'duration', i.e., something like
`date1 < date2  + 20 days`

As far as I know, I should be able to use either `xsd:duration` or `xsd:dayTimeDuration`, but using either throws an error related to a missing column name.

For instance, this query: 

```
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT ?test
WHERE {
    ?a ?b ?c
    BIND ("PT120M"^^xsd:duration as ?test)
}
LIMIT 1
```
Throws a `Virtuoso S0022 Error SQ200: No column PT120MD.`
Same with basically any example from [xsd:dayTimeDuration](http://www.datypic.com/sc/xsd/t-xsd_dayTimeDuration.html)

Am I missing something on the syntax? (It does seems to work on the paid version).

I can manage by using either a direct addition (`dateTime` + a number of seconds), or `bif:dateadd`, but I'd rather not use an engine-specific solution if I can avoid it.

(I tested by directly building from the current main branch, and by using a docker image based on 7.2.9)
--- end body ---
