Madhyaanhikaa is required to be done only after performing Madhyaanhikaa Snaan (Midday bath). It is not possible for each one of us to comply with all the rules prescribed in the Shaastra in the present circumstances, unless one has very strong will power, Shraddhaa and determination to adhere to the provisions in Shaastra, come what may.

How to decide the period of Madhyaanh? Assuming that the duration of daytime is 12 hours and 30 minutes at a particular place and if this duration is divided into 5 parts, the first part is called Praatah Kaal, to be followed by Sangav Kaal, Madhyaanh Kaal, Aaraahn Kaal, and Saanya Kaal. Thus at a place where sun rises at 6 am and sets at 6-30 pm, 11 am - 1.30 pm represents Madhyaahn Kaal.

And within Madhyaanh Kaal
the first one-third is called "Gandharv Kaal",
the second one-third is called "Kutap Kaal" and
the last one-third is called "Rauhina Kaal".

The best time for performing Shraaddh according to Shaastra is the Kutap Kaal (11.50 am - 12.40 pm in the above case). Since Shraaddh is required to be preceded by Madhyaanh Kaal, the right time for performing Madhyaanhikaa is between 11 am and 11.50 am for the place with sunrise and sunset as mentioned above.