The Congress Bridge Bats make their nightly departure 30-60 minutes before sunset. During bat season this can range from 7:30PM - 9:00PM because the sun sets at different times through the year. Check the local sunset time in Austin and plan to get there 90 minutes before so you get a good seat. Catching an Uber is affordable. This colony is estimated at 1.5 million Mexican free-tail bats.