machining time calculation

There are too many variables to give you a decent answer with so little information that you have provided.

If you are serious and will be doing a lot of these calculations then I would suggest software such as this:

http://www.cncci.com/products/mepro.htm

If this is only a one-time calculation - you need to provide a lot more information,

you can use the CAM progrom to calculate the machining time.