Tinito,
Not all Air Force pilots pull 12 hour days... but virtually all US fighter pilots do. It's demanding; you skip meals, shift your schedule several hours right or left from week to week, even spend "time off" thinking and planning for the next day(s). To answer your question in more detail, a flying day might look like this:
Show up to work: Anywhere between 0500L and 1100L (depending on Day/Night week)
Mission prep and brief: 2 hours
Step, start, taxi, takeoff, mission, land, taxi back, shutdown, fill out maintenance forms: 2.5 - 3.5 hours
Mission review and debrief: 1.5 - 3.5 hours (unless it's a FLUG-1, then it could reach 5+ hours
Queep: however many hours are left until you reach 12 hours from your show time the next day: 0 to 5 hours
A non-flying day might look like this:
Show up to work: Anywhere between 0500 and 1100
Perform Supervisor of Flying duties, vault duties, or other ground related activity: several hours
Stick a pencil in your eye: 1 minute
Wish you were flying: all day
Daydream about what it must be like for ANG Viper Pilots: 10 minutes
Queep: All the minutes you have available until you reach 12 hours from your show time the next day.