I think you are referring to the concept of Hora. If you’re talking about a different concept which sir has taught in some old video, please share the link.

Hora belongs to 7 planets (leaving out Rahu and Ketu from Navgraha). The Vaar/day is actually decided based on the Hora at the time of sunrise.

Yeh ek cyclical order mein chalta hai, jo ki anya graha ki prithvi se duri par aadhaarit hai. Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon – that is the order.

Next, to find out the hora at a particular point of time in a day, there are 2 methods:

Method 1: there are 12 horas from sunrise to sunset, and 12 horas from sunset to next day sunrise – so divide dinman (day duration) by 12 – that will be duration of each hora during the day, and similarly divide ratriman (night duration) by 12 and that will be the duration of each hora in the night. The first hora of the day starts at sunrise, and the first hora of the night starts at sunset.

Method 2: there are 24 horas from sunrise of today to sunrise to tomorrow. Take the entire duration between sunrise to next sunrise and divide by 24 – that will be the length of each hora, and sunset plays no role in this method.

Note – Method 1 is the appropriate one. I have given method 2 because it is used in some places and we should be aware.

The first hora on any day is the hora of the day lord (this is the reverse of the actual concept, but I’m saying it this way because it is easy to remember in the start) – eg on Thursday the order of hora will be Jupiter, Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter, Mars, Sun, Venus, and Mercury. Then, from the time of sunset, continue the series with Moon, Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter, Mars, Sun.

After Sun, the next hora will be of Venus but that will start at sunrise of subsequent day, hence the subsequent day will be Shukravaar.

Note – series of hora will remain the same on each day, but the hora at sunrise will change hence everyday the hora will fall at a different time (as per the western time concept which we use). Like 1st Jupiter hora may be from 6:05 AM to 7:10 AM on Thursday, but 1st Jupiter hora on Friday could be from 10:00 onwards.

Also note that the duration of each hora will vary because dinman and ratriman vary (day to day changes are not huge, but month to month or season to season changes are notable).

If you don’t want to calculate on hand, then some panchang/astrology apps and websites have it listed readily.