Over all length?
Must be long enough to work through action - if any - and,
Short enough to fit and function in the magazine or cylinder.
Length of case can affect chamber pressure. If a bullet is seated out 'long' the chamber internal volume is greater and therefore a given powder charge will burn with less pressure. If a bullet is seated 'deep', the chamber internal volume is reduced, resulting in greater pressure. In most handguns, this isn't too meaningful until the bullet is jammed down on the powder charge.
Loading a rifle bullet 'long' reduces internal volume, but if the bullet is wedged into the leade, that retards movement of the bullet and raises chamber pressure.
In any event, don't work up a load and then change ANYTHING without started from the bottom again.
Having a number of rounds loaded with differing seating depths can influence accuracy, but with a handgun, usually the difference isn't noticeable.