#JavaScript (ES6), 73 56 54 bytes
Getting the ball rolling; more golfing to follow ...
Takes input as an array of 4 integers ([h1,m1,h2,m2] in 24 hour format).
([g,l,h,m])=>Math.min(2+h+m,h-g+24*(h<g)+m-l+60*(m<l)) #JavaScript (ES6), 73 56 54 bytes
Getting the ball rolling; more golfing to follow ...
Takes input as an array of 4 integers ([h1,m1,h2,m2] in 24 hour format).
([g,l,h,m])=>Math.min(2+h+m,h-g+24*(h<g)+m-l+60*(m<l))