Once you’ve figured out how many rehearsal hours your play’s length requires, the following issues may warrant adding some time.  How much extra time depends on the actors involved and the demands of the particular play.  Here are some blocking considerations you might want to think about when planning your rehearsal time:

Fights and Dances.  Be they swordfights, fist fights, wrestling matches, or slapfests, any “fight” needs to be choreographed and rehearsed like a dance.  As for dances, sometimes even straight plays will have a single musical moment requiring coordinated action (e.g. The Fezziwigs’ Christmas Party in A Christmas Carol).  Choreography takes repetition to become seamless and natural; the complexity of the physical action and the coordination of the actors will determine how much extra time is required.

High levels of physical activity.  Physical activity that involves lots of props, like setting a table for a formal dinner for eight, usually requires coordinating the activity with dialogue.  This is like rubbing your belly while patting your head, and so takes a bit of extra time to make it run smoothly.  Reasonably complicated physical activity that doesn’t involve dialogue, such as scene changes made by the actors or complex physical business that either moves the plot forward or else is used for comic relief, usually requires extra time, too.  It requires a memorization of movements that can really only be learned during rehearsals.

Crowd scenes.  Any time you have more than four people on stage, it’s almost a dance to move them around.  Even one scene with six to eight people moving around over the course of six pages can add enough complexity to require extra attention.

Farces.  Because of the number of slamming doors typically found in farces, as well as the need to have exquisitely timed entrances or other physical movements (double-takes, etc.), farces usually take at least one week longer than other plays.  Farces often are longer than two hours in playing time, as well, which also means extra time.

Miming.  Not everyone is good at mime, and even if you have some talent for it, you probably don’t do it much.  Or at least, you probably don’t usually mime whatever motions the play you are in requires.  Some of this is work you’ll need to do at home, but sessions where the actors get feedback on their miming is usually a good idea if you want to really make them completely believable.

Card games.  You might not think of a card game as requiring blocking, but it does.  Plays like The Gin Game and Born Yesterday have dialogue that refers to certain things happening in the card games the characters play.  Learning when to draw and discard, when to deal, and when to shuffle your cards around in your hand, all while saying your lines, takes repeated practice to make it happen effortlessly.  The challenge is made all the more difficult because the cards you are looking at aren’t going to be the ones that are actually in the character’s hand.  That is, you may call “Gin” when you don’t actually have “Gin.”

Sleight of hand.  Magic tricks, juggling, and other similar special abilities need extra rehearsal unless the actors cast are already skilled in them.  While the actor responsible will need to practice the skill at home, integrating it into a scene where other things are happening is an extra challenge.

The blind.  If your character is blind, as is Susan in Wait Until Dark, you need extra rehearsal time to learn to move around the set as if you can’t see a thing.  Wait Until Dark and Black Comedy also have scenes where the stage lights are completely extinguished, but the actors have to move around the stage and do very specific actions in the dark despite not being able to see.  It takes extra practice to get so familiar with the floor plan that you can make this sort of scene flow smoothly without hurting yourself.