The 48 minutes (2 naligai) during both Sunset and Sunrise are called as "Kala Sandhi". The 24 minutes (1 naligai) before the Sunset and Sunrise and 24 minutes (1 naligai) after the Sunset and Sunrise comes under this "Kala Sandhi".
You must get the actual Sunset and Sunrise time from the Panchangam.
This "Kala Sandhi" is a highly inauspicious period for the following reasons.
1. Any baby born during this period are likely to get affected by this Kala Sandhi.
2. The Horoscope are likely to give confusing results in the future.
3. The preganant woman and infant babies under the age of 1 year must not be taken out during this time. We should not allow the shadow of any bird flying above falls on the baby.
4. The "Kala Sandhi" period should be avoided for starting a long journey.
5. The "Kala Sandhi" period is not suitable for conducting any type of auspicious functions.