[muhehe]

Basically every camera I have had has a "bulb", which is pretty much as-long-as-you-want exposure. Never heard of sensor overheating even after hours of exposure.

[Manuel_D]

Overheating is more of an issue for the image processor, at high frame rates. During bulb mode, the sensor is on for a long time but it's only one frame being handled by the image processor.

[buildbot]

Any CCD based camera will certainly heat up a lot, and cmos as well to a lesser degree without good/active cooling.

Most cameras time out at about an hour maximum unless they are special purpose astro cameras.