You can safely move the hands forward. When moving the hands past the number twelve, wait until the clock has finished striking the hour before moving on.
* Some grandfather clocks come with moon phase and / or day count discs. When you adjust these discs, wait until they are unmeshed from the clockwork mechanism. Usually, they are meshed with the clockwork between 5 pm and 7 pm or between 11 pm and 1 pm. So avoid adjusting the moon phase and day count at these times.
Your clock may work a bit differently, so experiment to find out when the discs are unmeshed from the rest of the mechanism before making adjustments.
* As your long case clock runs for several days, you may find that it is gaining or losing time. To set this right, you need to alter the length of the pendulum.
To slow down the clock, increase the length of the pendulum. Usually, you’ll find a nut at the end of the pendulum bob. When you turn the nut downwards, the bob will move downwards thus increasing the pendulum length. Move the nut upwards to make the clock go faster.