You really do not want to wait to fix this. By running your engine with a failed t-stat, it the engine takes far longer to reach operating temp, and struggles to stay there (if it ever gets there at all in Illinois in the winter). This causes it to run rich for a long time, which is not only bad for the environment (and your pocketbook - due to poor fuel economy), but is hard on the engine, oxygen sensors, and catalytic converters. I'd fix it.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild