Spoiler alert: it’s not a single number. Gatwick has two terminals, North and South, and each has its own short-stay zone. At Gatwick North, short-stay means you can park for up to 2 hours. At Gatwick South, you get a bit more breathing room—up to 3 hours.
Why the difference? Nobody knows for sure. Maybe the North terminal is just in a hurry. Or perhaps the South terminal likes to linger over a second coffee. The mystery is part of the fun.