You can chose to use the meanings for the numbers of the hours, as in 7:00 is the same as the number 7, or you can work it out according to the planet that is ruling at that time.  For this you will have to find out what time the sun rises in the morning.  (The weather report sometimes has this information for the following day, and fishing shops may have that information also) The hours of Magick start at Sunrise with hour 1. For example, if Sunday's sunrise is 6:15 a.m. From 6:15 - 7:15 is Hour 1, and is ruled by the Sun (Because it is Sunday). The hour from 7:15  to 8:15 is hour 2,  which ruled by Venus etc. Monday’s sunrise may be at 6:22, which makes hour 1 from 6:22 - 7:22 but is now ruled by the Moon. Each day's first hour is ruled by itself. It then runs through the chart until the next days ruling planet takes over and begins again.  You may choose to do a spell on a particular hour so that the Planetary power can be added to the spell.
 

More information about spellcasting can be found in  "Obsidian's Book Of Shadows", from Obsidian's SpellCasting booklet or from Obsidian's Classes.  Available from:.