The best way is to take the evening bus from Burgos, stay two nights and return on the second morning.
The mass times are as follows (check them when you get there)
Canto gregoriano
LAUDES A las 7,30 h. diario. 8 h. Domingo
MISA A las 9,00 h. diario. 12 h. Domingos y Festivos
VISPERAS A las 19,00 h. todos los días.
COMPLETAS A las 21,30 h. diario.