Incorrect error for plus/minus operations over timestamps and dates

[DDtKey]

Describe the bug

If you would try to perform plus/minus operation over dates/timestamps inside SQL it will return an error:
X - Y can't be evaluated because there isn't a common type to coerce the types to

It looks incorrect to me, it's more about unsupported operations (it works only with intervals), not coercion itself.

Moreover it confuses me, because it could be the same types and error doesn't report the relevant reason.

To Reproduce
Just write SQL with this unsupported operation, like:
select now() - now() from x

Expected behavior
It should returns clear error, like: the Timestamp - Timestamp is unsupported operation

Additional context
Here the current logic is: Link to the related code