Classic Mac OS support (both 68k and PPC): OS X 10.0 was released March 2001, dropped with 10.5 released October 2007. So about 6 years, 8 months.
PowerPC Mac OS X app support: First Intel Mac January 2006, support dropped with 10.7 in July 2011, so 5 years 5 months.
32 bit iOS app support: iPhone 5S with 64 bit CPU released October 2013, 32 bit app support removed in iOS 11, September 2017, so 3 years 11 months.
32 bit Intel app support (and Carbon framework): Mac OS 10.5 was first to allow 64 bit GUI apps[1], in October 2007, 32 bit support dropped in 10.15, released October 2019, so 12 years.
I'd probably count this nearer to the first three than the kinda drawn out 32 bit to 64 bit Intel transition, so perhaps about 4 years?
[1] There was limited 64 bit support before in 10.4.