I can't speak definitely, but I'm pretty sure they will be okay for 4-5 hours.
My house is kept at 62°F at night and when we aren't home. My 2 bantam chicks are brooding in my house. I did the same thing as you when my chicks were 2 weeks. Unplugged the heat lamp when home, forgot to turn it on when I left. I was gone for 7 hours. The thermometer gun read 63°F throughout their brooder when I got home. They were just fine. I did turn the light back on immediately when I got home.
I also kept them off heat all night starting at 4 weeks. They did perfectly fine.
My house is kept at 62°F at night and when we aren't home. My 2 bantam chicks are brooding in my house. I did the same thing as you when my chicks were 2 weeks. Unplugged the heat lamp when home, forgot to turn it on when I left. I was gone for 7 hours. The thermometer gun read 63°F throughout their brooder when I got home. They were just fine. I did turn the light back on immediately when I got home.
I also kept them off heat all night starting at 4 weeks. They did perfectly fine.