Focus held over an extended period of time is called Sustained Focus and involves short-term memory and higher levels of arousal and motivation.
Sustained Focus:When the time duration for Focused Attention becomes extended, a new factor is introduced into the attention process: the ability to maintain a consistent level of performance which involves short term memory.
Here's where the terms "vigilance," "attention span," "working memory" and "concentration" are often applied.
I might, for example, give you a rather long string of numbers and ask you to raise your hand when you hear the number 4 followed by the number 7.
The length of the task will require higher levels of orientation, short-term memory and motivation. The more difficult the task is made, the slower the perceptual process may proceed and the more liable the process will become to breakdowns.