Varam:- The vaaram or day for astrological calculations as you all know begins at sunrises and lasts till next sunrise. So it is contrary to the normal calendar days we follow which is from mid-night to mid-night. I think I have already explained how days are derived as per hora- Shahstra ( i.e. the ruling hora at sun rise of a particular day makes that day) like Sunday belongs to Soorya (Bhanu) so becomes Bhanuvasaram, Monday Soma vasaram etc. As we know every planets hold certain characteristics, the day we choose for a particular occasion should also indicate or relating to the characteristics of the ruling planet for that particular event.