-- Answer: False --

Neither the Philippian jailer nor the eunuch rejoiced in Christ until after his baptism. Why? Because it wasn't until he came up out of that watery grave of baptism that he was then able to "walk in newness of life" (Rom. 6:3,4), and be a "new creature" in Christ Jesus (2 Cor. 5:17).

Yes, they rejoiced after their baptism because that is when their sins had been forgiven (Acts 2:38; 22:16) and they were, thus, saved from them (Mk. 16:16; 1 Pet 3:21).