All are important but we will mostly talk about CPU time in 367. This depends on the machine, compiler, etc. as well as the code. Complexity affects performance but not the other way around.
Some methods perform the same number of operations every time they are called.
Other methods may perform different numbers of operations, depending on the value of a parameter or a field. For example, for many of the Sequence methods, the number of operations depends on the size of the sequence. In the worst case, all of the items in the array must be moved. Therefore, in the worst case, the time for addBefore is proportional to the number of items in the sequence, and we say that the worst-case time for addBefore is linear in the number of items in the sequence. For a linear-time method, if the problem size doubles, the number of operations also doubles.