Keep in mind these requirements are distinct; you may go well over the 4,500 hours but still not meet the duration requirement if those hours were not spread over a three-year period. For example, assume you worked on two projects at the same time, over a two-year period.
Nicotine is the main ingredient of concern in smokeless tobacco. It is estimated that a normal, 30-minute dip of smokeless tobacco delivers the same amount of nicotine as 3-4 cigarettes. Nicotine affects the brain and central nervous system and changes neurotransmitters levels regulating mood, learning, alertness, and ability to concentrate.
You are affected in your lungs from cigarette smoking. Chew (dip) will just affect your lip/teeth/gums. You will have negative affects from the cigarette smoking for some while. But no, chew wont affect your running abilities. Lots of professional athletes that need a nicotine fix chew.