Domain based on TIMEZONE WITH TIME ZONE

I'm using a domain to specialize the built in TIMEZONE WITH TIME ZONE type. I want to sanity check this approach before continuing to use this.

I want to prevent timestamps with non-UTC offsets from getting inserted into the database. Having a UTC-only database at the schema level means no app, proc, script or load operation can inadvertently supply a local time offset.

The domain is defined as:

CREATE DOMAIN UTC_TIMESTAMP AS TIMESTAMP WITH TIME ZONE CHECK (EXTRACT(TIMEZONE FROM VALUE) = 0);

CREATE TYPE UTC_RANGE AS RANGE ( SUBTYPE = UTC_TIMESTAMP );

My potentially misguided assumption is that I am effectively re-using a check constraint across the schema.

Is this crazy?

Am I missing the point of how Postgres stores TIMEZONE WITH TIME ZONE internally?

Thanks in advance,

Ben