Calculate work hours

I have a table with a date time column which actually stores the data as and when it is inserted. I need to calculate the time the machine has worked hourly wise. For example the table contains records from 13:00 to 13:15 and 13:45 to 14:00 i should get 30 mins as working time....

Hi Varmacorp,
Can you explain what is the relation between the consecutive datestimes?
Maybe post more examples, like "What times don´t you consider a valid interval"..