Welcome to the forum, CBB
What system do you have?
What Voice Mail system?
Do you know the versions for both?
Automatic forward by time is not part of the Norstar. But you can set it up through the voice mail. Either in the persons mail box or through the Auto Attendant/CCR tree.
For the mailbox, you would need to include "to be forwarded to my cell press x".
For a better Time Control you can use the AA/CCR funtion of the voice mail. Depends on the VM unit. Let us know what you have. It would be best to bring in a technician to assist you in programming it for you. Check this web site for a tech near you.