Probably the same as any other major... probably even shorter than some (such as pre-med), so 4 years. For my school, you need Intro, Research Methods, Stats, 6 electives and 3 courses from another social science (I chose anthropology, but you can do political science, economics, psychology, etc).
1 Rubisco, the enzyme that is responsible for carbon fixation (combining CO2 with RuBP), can also add O2 to RuBP. 2  When the O2 concentration within a leaf becomes greater than the CO2 concentration, rubisco will add O2 to RuBP instead of CO2.  The resulting molecule cannot be used in the Calvin cycle.
C4 photosynthesis is named as such because the fixation of carbon dioxide, by an enzyme called PEP carboxylase, results in a four-carbon sugar. The carbon acquired this way is then passed on to RUBISCO and enters the Calvin cycle.