Need help for condition

Hello All   I have an order with the time 08/03/2015 7:30 08/03/2015 10:30   I have availability with the time 08/03/2015 07:00:00 to 08/03/2015 19:30:00   Here the availability falls for 3 hours only for the order. 
My requirement is that  If the availability falls between the order time ,For order if availability< 4hours I don't want to show employee.   How to apply the condition.