ISR time will count towards your total time... but like a few others have said it won't help much at the majors, the regionals would be better for that. You are pretty much going to have to wash through a regional on your path unless you get some more serious type rating in a jet and not turboprop and have a connection with someone in a major that can pull some strings.

So although the ISR would be fun, it will be a longer path to get you where you ultimately want to go.