My Spanish is pretty weak, but according to the observatory's website,
they transmit a time signal during two 25 minute periods each day
between 10:00 and 11:00 utc on 15006 khz and 4998 khz.

Here's the actual Spanish, in case I'm interpreting it incorrectly:

Transmisi=F3n de se=F1ales horarias en HF, durante dos periodos de 25
minutos diarios, en 15006 y 4998 KHz. Respectivamente, entre 10:00 y
11:00 horas UTC.

Might be worth a listen.