THE ANCIENT LITURGY OF THE HOURS 

The day's seven Hours noted above from Saint Hildegarde's Medieval manuscript, Physica,
refers to the ancient Liturgy of the Hours prayer meditation.
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The  Liturgy of the Hours are the seven prayer times appointed for each day, a ritual which dates back to ancient times.  
In the monastic tradition, these meditations are traditionally categorized as:

1. Matins/Lauds
2. Prime
3. Terce 
4. Sext
5. Nones
6. Vespers
7. Compline

These set times for prayer are ordered around the canonical calendar according to hour, day, and week of the year.
This ancient ritual offers new channels of meditation for every calendar day.  
Traditionally, the Prayers are chanted audibly or silently from the heart.