Note the methodological similarities between calculating Witchcraft's planetary hours and calculating Judaism's halachic hours. Both Witchcraft and Judaism use these time calculations to determine the best time to do ritual work.
CALCULATING PLANETARY HOURS
Source: Bewitching Ways
The planetary days are divided into 24 planetary hours with the first hour of the day beginning at sunrise and the last hour of the day ending at sunrise of the next planetary day. The period that extends from sunrise to sunset (daylight) is divided into 12 hours and the period extending from sunset to sunrise of the next day (nighttime) is also divided into 12 hours giving the 24 hours of the planetary day. However, the term Hour does not necessarily mean 60 minutes.
These influences can either help or dissolve your effort so it is important to calculate carefully.
Your planetary hours are specific to your exact location. In order to calculate your planetary hours, you will need to know the sunrise and sunset for your area. You can get this from your local newscast, newspaper or online.
Now comes the math.
1. Figure out how many minutes there will be between Sunrise and sunset
For example, say the sunrise is 6 a.m. and sunset is 8 p.m. There would be 840 minutes of daylight.
2. You then divide that number by 12 to get the number of minutes in each planetary hour of the day.
840/12= 70. So, each day planetary hour in our example would be 70 minutes long.
3. Divide your day hours into planetary hours using the minutes as your guide for increment
hour 1 in our example: 6-7:10 a.m.
Hour 2: 7:10-8:20 a.m. etc.
4. Repeat process for time between Sunset and Sunrise (for the next day) to figure out your night planetary hours.
CALCULATING HALACHIC HOURS
Source: Halachic Times (original source taken offline, info abstracted from earlier Craftwork Of A Jewitch entry, new source - from Ask Moses - What is 'Halachic Time' or a "Halachic Hour'?)
The normal calendar that we use divides a day into 24 equal hours. Normally, noon is approximately the midpoint between sunrise and sunset, and of course midnight is approximately the midpoint between sunset and sunrise. This is thrown off, of course, by daylight savings time and other minor factors.
The "Jewish day" (daytime part) divides the time between sunrise and sunset into 12 equal parts that are often called "halachic hours". Since on average, sunrise is around 6am and sunset is around 6pm, we can call sunrise "Halachic 6am" and sunset "Halachic 6pm". This will then make it easy to describe the 12 halachic hours of daylight.
The times for morning, afternoon, and evening prayers are based on the notion of the halachic day. Also, the times for the start and end of the Sabbath, fasts, etc.. all use the Halachic day, although in some cases fixed times are used. For example, candlelighting on Friday night is always 18 real minutes before sunset, not 18 halachic minutes.