Most dashcams can record forever if you like, in general they start recording as soon as they get power and stop when you cut power, so in regard to footage saved it is only the size of the memory card that have a say in how many hours of footage you have saved, and if you are in a car how long your car battery will last ( you should not go under 12.2 volts on a car battery, at least not often )
BUT ! you can not do this in a car parked in the sun, the car get very hot and that + the temperature of the camera mean it will shut down due to high temperatures soon.