ETA

As a naval communicator, the really stressed keeping your message short, and concise. The idea was, the less you transmit, the harder it is for the enemy to home in on your signal.
Ambulance personel have no enemy (in theory), but I think the time they spend talking to the base, is time they could be tending to their patient.
When I hear a transmission much like: "Our ETA is gonna be approximately 10 minutes."
ETA means estimated time of arrival, which eliminates the need for the word approximately. If you think about it, you also don't need the words, "gonna be." You would not be reporting somebody else's ETA, thus no need for the word, "our."
You could say, "Eta 10 minutes."