The actual arch will stay up for a while (given there's no heavy wind)-- it's the balloons you'll need to be careful about. Heat from the sun can cause the balloons to pop after a few hours. So just keep that in mind. I've only made a balloon arch on the 4th of July when it's really hot, so if you make it in cooler temps, leave a comment and let us know how long it lasts. I'm betting that inside or cooler temps will help the balloons to stay in place much longer without direct sun on them.