In which time Moses was born, and was exceeding fair, and nourished up in his father's house three months: And when he was cast out, Pharaoh's daughter took him up, and nourished him for her own son.Which agrees with Exodus 2:2 (and Hebrews 11, this period of time being three months is said three times in Scripture). Three months separated the Birth of Moses from him being taken in by Pharaoh's Daughter.
But Stephen goes on to evenly divide the rest of Moses life into three periods of 40 years. 40 years in the house of Pharaoh king of Mizraim, 40 years in the house of Jethro, and then the 40 years of the Wilderness Wandering.
The Forty years of the Wilderness Wandering began in Nisan, the Nisan of the First Passover, and ended in a Nisan, the Passover recorded early in the Book of Joshua. It seems reasonable then to infer all three 40 year periods begin and end in mid-Nisan.
Just looking at the account of Pharaoh's Daughter finding Moses in Exodus 2, there are good reasons to suspect this is happening near the Spring Equinox.
So if Moses was born three months before events that happen near the Spring Equinox, then he was born near the Winter Solstice.
Likewise, three months means he was taken in by Pharaoh's Daughter at about the anniversary of his Conception.