Function inserting into tstzrange ? (syntax error at or near...)

I'm sure I'm doing something stupid here, but I think I've got the syntax right ?

The error I'm seeing:
psql:event_session_funcs.sql:26: ERROR:  syntax error at or near "["
LINE 11:         VALUES(p_event_id,[p_start_time,p_end_time)) RETURNI...

The function:
CREATE OR REPLACE FUNCTION new_event_session(p_event_id text,    p_start_time timestamptz,
    p_end_time timestamptz,
    p_sess_title text,
    p_sess_desc text
    ) RETURNS text AS $$
DECLARE
v_session_id text;
BEGIN
    INSERT INTO event_sessions(event_id,evt_sess_times)
        VALUES(p_event_id,[p_start_time,p_end_time)) RETURNING evt_sess_id INTO v_session_id;
// REST OF FUNCTION REMOVED FOR BREVITY

The table definition:
CREATE TABLE IF NOT EXISTS event_sessions (    event_id text NOT NULL,
    evt_sess_id text NOT NULL PRIMARY KEY DEFAULT ksuid_pgcrypto_micros(),
    evt_sess_times tstzrange NOT NULL,
    evt_sess_inserted timestamptz not null default now(),
    CONSTRAINT fk_evt_id
    FOREIGN KEY(event_id)
    REFERENCES events(event_id),
    EXCLUDE USING gist (
        event_id WITH =,
        evt_sess_times WITH &&
    )
);

N.B. I'm calling from Go, the library does not natively support tstzrange, hence the need to break-out the input parameters.

Thanks !