At what point does the Mass start and end?

[savedbychrist]

For Ordinary Form, the Mass ends at “Ite missa est, Deo gratias”, but I’m not sure if it starts at the Introit or the Sign of the Cross.

For Extraordinary Form, I’m not sure about both ending and starting. Does it start with the Sign of the Cross (which means prayers at the foot of the altar is included), or the Introit (which is after prayer at the foot of the altar)? And does it end at “Ite missa est, Deo gratias”, or Last Gospel? (Or final blessing???)

 

[Canvas]

I think about the Mass from procession to procession, essentially. This may not be theologically correct, but I try to get there before the Priest processes in, and wait until the Priest has processed out before leaving.