? which calendar is that from myzmanim says either 2:35 or 4:06
According to the opinion that dawn is when the sun reaches 16.1° below the horizon, during the summer months in the northern locals, where the sun doesn't go that far below the horizon altogether, anything that needs to be done before dawn, needs to be done before midnight and we use the time of midnight as the time of dawn.
Based on the Siddur of the Alter Rebbe by Sefiras Ha'omer.