The After Effects time expression is a great way to add movement without setting keyframes. Here’s how it’s done.
If you’re new to expressions in After Effects, one of the most helpful and easy to use expressions available is the time expression. Essentially, the time expression returns a number value related to your current position in the timeline. For example, if you were at three seconds, the time expression would return a value of three.
How to Use the Time Expression
The time expression can be thought of as a variable in itself. Like we said before, it will return a value related to position of your playhead in seconds. For most motion graphic circumstances, you will likely want to multiply the time expression so that it returns a larger value. In that case, we will have to tell After Effects to do some basic math.
In order to use the After Effects time expression, select the property in which you want the time value to affect and option click on the corresponding stopwatch. For example, if you wanted to set the expression to affect the position, simply click the stopwatch to the left of the position text.
Next, you will need to add in the time expression into your expression. You can simply replace the default text in your expression with the word time or you can have it interact with the time expression by using basic math icons like (+,-,/, & *).
To link your position to the current time, simply option click on the stopwatch next to corresponding position property. In the example above, we separated the x and y position so we could apply the time expression to just the X position. Once you hit the stopwatch, you can simply type in time* any value.
To link time and rotation together, simply click on the stopwatch next to rotation and replace the current expression with time*any value. In the example above, we have a five second loop. So, using some simple math, we figured out that we would need to multiply the time by 72 to create a perfect loop.
You can also multiply time by itself so that it will increase exponentially. Simply option click on the stopwatch next the the property you want to effect and type in time*time. In the example above we multiplied time to the power of four.
You can also link the value of text to be that of the current time. Simply option click on the stopwatch and add in the time expression. By default, the numbers will include numbers beyond the decimal point, so it is recommended that you use the Math.round() function to round up to the nearest whole number.