What is Horai?
Horai are independent time slots of approximately one hour duration, that occur throughout the day, where one planet is rules per hourly slot.
The day starts at the moment of sunrise and ends just before sunrise the next day. The daily starting horai will be the horai of the planet ruling that day. So, if it is Monday, then the starting hora at sunrise will be the moon horai. Then the horai changes in a particular order till around 1pm where the horai of the day again occurs.
What are the horai?
Arka [Sun], Sukra [Venus], Budha [Mercury], Chandra [Moon], Mandha [Saturn], Jeeva [Jupiter], Dharasudha [Mars] are the 7 horais, in their proper order of occurrence.
Astrologers generally advise that it is better to know the qualities of these planets and have activities related to that planet scheduled for the day to get maximum mileage out of those activities.
For example, your debts will be cleared soon, if you return part of your debt on Mars Horai, on Mars's day [Tuesday]. Not too difficult to follow, but worth a try, isn't it. If it works, it works.
ePanchang features an online Horai Calculator to calculate Daily Hora and also displays Hora Chart for users to check; this is a free service available in all cities