Basant Panchmi is celebrated on the fifth day of Shukla Paksha of the Hindu month Magh. From this day, Vasant Ritu (the spring season) begins in India. This festival is celebrated when the Panchami Tithi prevails during the first half of the day i.e. the time between sunrise and midday.
The celebration can only shift to the next day in one condition i.e. if Panchami TIthi is not prevailing in the first half of the first day at any point of time. Otherwise, in all other cases, the celebration will take place on the first day. That is why, sometimes, Basant Panchami also falls on the Chaturthi Tithi as per Panchang.
On this day, Lord Kamdev and his consort Goddess Rati and are worshiped in 16 ways (Shodhashopchar Puja) during the time between sunrise till midday.
Astrological Importance -
If husband-wife worship Rati-Kamdev after this Sankalp in 16 ways (Shodashopchar), their married life turns into a blessing from all the possible ways.
Shodshopchar Puja Sankalp
ॐ विष्णुः विष्णुः विष्णुः, अद्य ब्रह्मणो वयसः परार्धे श्रीश्वेतवाराहकल्पे जम्बूद्वीपे भारतवर्षे, अमुकनामसंवत्सरे माघशुक्लपञ्चम्याम् अमुकवासरे अमुकगोत्रः अमुकनामाहं सकलपाप - क्षयपूर्वक - श्रुति - स्मृत्युक्ताखिल - पुण्यफलोपलब्धये सौभाग्य - सुस्वास्थ्यलाभाय अविहित - काम - रति - प्रवृत्तिरोधाय मम पत्यौ/पत्न्यां आजीवन - नवनवानुरागाय रति - कामदम्पती षोडशोपचारैः पूजयिष्ये।
ॐ वारणे मदनं बाण - पाशांकुशशरासनान्। धारयन्तं जपारक्तं ध्यायेद्रक्त - विभूषणम्।। सव्येन पतिमाश्लिष्य वामेनोत्पल - धारिणीम्। पाणिना रमणांकस्थां रतिं सम्यग् विचिन्तयेत्।।
On this day, at the above given worship duration, intellectuals (or people related to education, art, etc.) worship Saraswati. The Puja becomes even more powerful when worshipers recite Saraswati Stotra along with the other rituals.