 Time is just distance divided by speed. The distance from Alice to friend 1 is L over 2 and the speed of light is C. So the time taken in between Alice turning on the light and the friend being dunked is L over 2C and the case is exactly the same for friend 2. Okay, so what about from Bob's reference frame? Now Bob is standing on the platform watching this train whiz past at velocity V. Now I'm going to make a crazy assumption. I'm going to say maybe, just maybe, Bob measures a different length for the train, which we'll call LB. Now this might not turn out to be the case. Maybe LB is equal to L, but I'll just keep this general for now. And in which case the space between Alice and one of Bob's friends is LB over 2. Now in Bob's reference frame, his friends are moving to the right at speed V. As is Alice. What are the times T1 and T2 that Bob records between Alice turning on her light and his friends getting dunked?