Expanding time - When you expand time in a film, you are increasing the duration of the footage you have. Although it is relatively rare to many films, it is often used for high action, fast paced shots in which you want to increase tension or draw the audiences eye to minor details.
There are various ways in which this can be achieved though the most common of these would be slow motion filming, in which the speed of the shot is simply drastically reduced.
Other techniques that can be used include the repetition of the same same shot from many different angles or time remapping, a technique which see's the the editor smoothly decreasing (or increasing in other cases) the speed of the shot at various moments, such as in numerous fight scenes in The Matrix.
Shrinking time - This is far more commonly used when compared to time expansion. When you shrink time, you are basically compressing the space of time in which an event happens to make it shorter than real time. There are many ways in which this can be achieved, some of which include:
Time Lapse editing, where filmakers simply speed up the footage they have by a considerable ammount. A good example of this would be in building construction videos, such as the creation of The Hogwarts Castle Model for the Harry Potter film series...
Time remapping can also be used again, but in a contrasting way, meaning film is instead intermitently sped up.
Another technique key to shrinking time in editing is the use of shots. For example, the editor may choose to use only a certain ammount of shots overall that represent an event, rather than documenting each and every part of it. This effectively cuts down the time that the sequence lasts and makes it quicker than real time.
Finally, cutaways can be used in order to represent aspects of the sequence, such as a dip to black or even B-roll footage. They simply exist to create understanding. This could mean that the audience is able to understand what is occuring in the scene but with a lot less shots.
Real Time - Literally as it is stated, real time means keeping a number of shots in a sequence that are parallel to a sequence that would happen in real life. This mostly means that the time taken in the filmic world is the same taken in the normal world for it to run. This is often used in dialogue scenes as the speed of the conversation takes place at a normal rate.
Along with this, the principal of match on action is frequently used beside real time in films, though it is not essential. Match on action basically means that each shot follows on exactly from where the previous one left off, so for example shot 1 may be of a ball in someones hands and shot 2 may follow from this by showing the ball moving towards another person.
Match on action is not essential however, as is shown by shrinking and expanding time; jump cutting to the ball landing in another persons hands after the shot of it stationary previuosly would be an example of this as we as an audience did not see that the actions matched- we simply assume from the second shot that the ball was thrown.
