Can you sign more than 1 Master Promissory Note Concurrently?
As far as I know, the way this is done normally goes something like this:


You apply to as many schools as you want. 
You hear back from them in a couple of months.
You are told that you have until a specific date to accept the offer,
which may be slightly different for all the schools you got accepted to.


This gives people a chance to evaluate (ideally) all their options before they agree to commit to a particular school. These deadlines are usually included in the acceptance documents you get in the mail, if they aren't listed online already in their admission timelines.

Best of luck!