I work on Friday nights so I can't pick up my daughter until Saturday morning.
Family Law Attorney
If both parents agree to the schedule change, then there is no problem with making adjustments to the court orders. However, if the custodial parent will not agree, then you need to make arrangements to pick the child up or have someone else pick the child up at the court-ordered time and place and schedule child care for time you are working.
Divorce / Separation Lawyer
I think that you are wanting to give up your Friday nights because of your work schedule. This should be no problem. Just write (email, text or letter) the custodial parent that you are intending to do this. Hopefully that will be enough. If the custodial parent ends up not cooperating, then you will have to go back to Court.
This information is not legal advice and does not form an attorney-client relationship.
If the parties agree to it then you can it. Strict interpretation is that you must pay for a baby sitter. Custodial parent would not be held in contempt if she did not make the child available on Saturday.