Time conversion

I use a software for my company called Team Viewer, which allows me to remotely connect to a customer. Well the sad part is the log file of it is the worst part about it. I've done a lot of work already for this company and retrieved all my log files, but the time is what is messing me up. Below is how it records the time. What would be the formula to figure out total time worked, because I have 245 cells to calculate time for :/

Connection Started: 21:16:15
Connection Ended: 22:03:40

time conversion

If we have in column a:
a1- Connection Started: 21:16:15
a2 - Connection Ended: 22:03:40

add column b:
b1 =MID(A1;20;9)
b2 =MID(A2;19;9)

column c:
c1 =VALUE(B1)
c2 =VALUE (B2)

and the result =C2-C1 (0:47:25)

the format of the cell b and c must be hour.