FIFO simply queues processes in the order that they arrive in the ready queue.
2.
However, once that barrier has been crossed, the time taken by that activity no longer depends on the time of day at which we decided to perform it . . . . It could be related to some sort of queuing process, but we prefer to see it as due to resource allocation ( attention, time, energy ), which exhibits a broad distribution : shorter activities are more likely to be executed next than the longer ones ."