On 22 June 2021 at 3:05 AM IST, Sun enters Arudra nakshatra and continues in same constellation for another 13 days. Initial 3 days which are 22,23,24 are important when sun in Arudra 1st paada.
In ancient days, these 13 days were called mensus dates of earth (bhoo devi). This is actually when Sun cross Mrigasira and enters Arudra (Moonsoon completely arrives in India) and summer solstice (longest day in year when Sunrays fall on earth for more time)
Out of these 3 days, 22 and 23 we can perform Rudra Abhishek )n 23rd rudrabhishek before 7am IST), on 24th (after 5AM IST), on 25th after sunrise.