Forever. Contrary to what you have been told CA does not have an expungement process. You can ask to have the conviction dismissed pursuant to PC 1203.4a but the arrest and conviction will stay on your record and a note will be added saying the conviction is dismissed.
A Governor's pardon shows rehabilitation and restores any forfeited civil rights but it does not erase your conviction. After all the pardon will say what you have been pardoned for doing.
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient... more
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.