I’d check with the people you are renting the truck from. They can often set you up with the SAT time as well. If not, they will know who to contact.
As for the listen line, I’m assuming that this is an extra audio line that goes with the SAT signal or over a separate phone line to the master control of the broadcast. It allows them to listen to the directer or producer of the live event and to know exactly when a break is coming. This allows them to insert their own material into the breaks and have it look reasonably clean.
Or it could simply be a phone line where the receiving station can dial in to verify that a signal is being uplinked at a given moment.
Not my monkeys. Not my circus.