Do not ritually slaughter a kosher animal and its young on the same day.
“Whether it is a cow or ewe you shall not slaughter it and its young on one day” Vayikra 22:28
If someone transgressed and did ritually slaughter them the meat is kosher.
The day goes according to nightfall (sunset to sunset)
Therefore, if a person slaughtered the mother animal at the beginning of the night of the 4th day he should not slay the young until the beginning of the 5th day.
If he slaughtered the mother animal towards the end of the 4th day, he may slaughter the young at the beginning of the night of the 5th.
This applies at all times and all places for men and women.