How does this work?

I was given an offer to interview at LECOM? I am still waiting to hear from another five schools, but I know they haven't received all of my letters yet! If Erie were to offer me a spot, how long do I have to decide? I don't want to turn down their offer, but I would like to see if I am offered an interview at the other schools too.

Also...does anyone know if Midwestern in chicago is still giving out interview spots? I just read in their catalog they have usually granted all interviews by Dec. 1!!!!!!!!