I changed oil and being "smart" I left the hood released but latched, thinking I was going to check level the next morning. Then sure enough I was in a hurry in the morning, skipped the level check, and forgot about the hood still released. I drove to work and drove back home in the evening, when I finally noticed the hood popped up. There was no sign or noise when I was driving with the hood released. I suppose there was no harm done but figure might as well ask here. Thanks!
The only thing would be if you hit a bump and released the hood the rest of the way and slammed open against your windshield! But obviously that didn't happen, so asside from an little added cool air flowing over the top of the engine, I don't see any other issues...
Your car is OK, the secondary latch is there for just that type of event. Way back in the olden daze, occasionally people would forget to latch their hoods and they would blow open on the highway which made a mess of the hood and sometimes the front of the roof. That was probably in the 1930s, but secondary latches weren't as reliable in the 1950s as they are now. I did see the occasional wind opened hood in the 50s and 60s