Here's why:

* Exposure to the atmosphere: Extrusive rocks are formed when magma erupts onto the Earth's surface (as lava flows or volcanic ash). This means they are exposed to the much cooler air and water, causing rapid heat loss.

* Increased surface area: Extrusive rocks often have a high surface area to volume ratio, further accelerating cooling. Think about how quickly a thin pancake cooks compared to a thick steak.

* Rapid crystallization: This rapid cooling leads to smaller crystals forming, which are characteristic of extrusive rocks like basalt and rhyolite.

In contrast: Intrusive igneous rocks, which cool slowly beneath the Earth's surface, have larger crystals.

While the exact cooling time depends on factors like the size and shape of the eruption and the surrounding environment, extrusive rocks generally cool much faster than intrusive rocks, often within days or weeks.