The time between Makar Sankranti and 40 Ghatis (roughly 16 hours for Indian locations if we consider 1 Ghati duration as 24 minutes) from the time of Makar Sankranti is considered good for auspicious work. This duration of forty Ghatis is known as Punya Kaal. Sankranti activities, like taking bath, offering Naivedhya (food offered to deity) to Lord Surya, offering charity or Dakshina, performing Shraddha rituals and breaking fast or Parana, should be done during Punya Kaal.
If Makar Sankranti happens after Sunset then all Punya Kaal activities are postponed till next day Sunrise. Hence all Punya Kaal activities should be done in day time.
DrikPanchang.com suggests Sankranti Muhurta which falls between Makar Sankranti moment and 40 Ghatis from it. We list this time as Punya Kaal Muhurta. Our holy scriptures suggest that 5 Ghatis duration after Sunrise (if Sankranti happens after Sunset on previous day) and 1 Ghati duration after Sankranti moment (if Sankranti happens in day time) are highly auspicious. If this Muhurta is available we list it as Mahapunya Kaal Muhurta. Mahapunya Kaal Muhurta, if available, should be preferred over Punya Kaal Muhurta.