The question "how long does iOS 2" likely refers to the duration of support or update life for iOS 2 or how long it takes to update to iOS 2. Here is what I found:

• iPhone OS 2 (the predecessor name to iOS) was released on July 11, 2008. It introduced the App Store and many new features.
• The updates for iPhone OS 2 continued through versions 2.1, 2.2, and the final 2.2.1 released on January 27, 2009. So the active support for iOS 2 spanned about 6-7 months.
• More generally, Apple tends to support iPhones with iOS updates for around 5-7 years, including major upgrades and security patches.
• For iOS updates installation in general, the update time varies based on update size, internet speed, storage, and device performance, with typical updates taking about 20 minutes to several hours.

So, iOS 2 itself was actively updated for about half a year, but Apple device software support across iOS versions usually lasts several years depending on the device model.

If the question was about update installation time instead, typical iOS updates take 20 minutes to a few hours depending on conditions.