I once had a roommate who would smoke up to a carton a day. No shit. He was a lazy, worthless piece of shit. He always had a butt in his hand, and would wake up in the middle of the night to smoke several cigarettes. Last I heard, that despite a massive heart attack and a quintuple bypass, he was still smoking.
I quit smoking more’n a decade ago… but when I quit smoking, the big antismoking trend was just really getting rolling. Every job I ever had was fine with smoking at work, with the exception of the psych hospital (it’d set off the smoke alarms).
I recall when I was a fry cook, in my early twenties, I often would stick a cigarette in my mouth, light it, and wind up literally having to breathe through it when things were really, really busy, and I couldn’t spare a hand to take it out of my mouth occasionally.
And no, I never got ashes in anyone’s food.
At least, not by accident.
No shit! I am not the kind of smoker who walked away from a lit one! 
I couldn’t stand to put out a cigarette with more than 1/4 inch left on it, but I suppose I did occasionally.
I smoked 2.5 packs a day at the end of my smoking period. If you figure I slept 8 housr per night, that left 16 hours of awake-time, minus 6 hours at my desk at work is 10 hours. 2.5 packs is 50 cigarettes, divided by 10 hours…
Damn, I was puffing away like a mad woman…
And although I never woke up to smoke, I did not get up out of bed until after my first one. I smoked while eating, driving, everything but having sex.
Going on 14 years since my last one, thank God. Miss 'em, though.
I used to be a freakishly heavy smoker - about 3 packs per day.
I worked in a restaraunt and I was the opener, so I would get there about about 6:45 am and start setting up stuff - I would blast through a pack (25 per, here in Canada) by 8:00 when the restaraunt opened.
Then, throughout the day, I could run up to the staff room, smoke an entire cigarette, and be back to my section in 4 minutes. Occasioinally I would slam into the walls on the way down from the break room, but I never actually passed out.
Then on my 30 minute break, I could smoke 4 cigarettes while eating a pancake (which is what I would always have on my break - one pancake with whipped cream).
Then I would finish up for the day at about 3:30, and pretty much be smoking non-stop until I went to bed. I never woke up in the night to smoke, but I’d light one before I got out of bed in the AM.
I quit 10 years ago this October. I still occasionally get the urge - then I think “gee, a smoke would be nice, except you would DIE!” - since quitting I found out I have asthma - even a wiff of smoke can set off an attack. I’m not sure how I was able to smoke so much all those years - the only thing I can think of is that my lungs were beaten into submission and just finally gave up.
I still smoke in my dreams though - when I first quit I would wake up and feel SOOO guilty - now I just enjoy myself. Sort of like the dreams where I’m having sex with someone inapropriate - it’s only a dream. 
I go through an average of about three packs a day. I smoke in my apartment, and in my car, and outside - almost continually. My breaks at work are about 5 minutes every hour, while I have a smoke.
I don’t smoke while I eat, cook, clean, or have sex. My smoking goes down noticeably if I am cooking something complicated, or if I’m all over a lady. I don’t get up in the night to smoke, though if I can’t get to sleep and get up to read, of course I smoke then.
I do not put my cigarette down and ignore it; oddly enough, one of my pet paranoias is fire - I attend to my smoke while it is burning.
I was smoking 2.5 to 3 packs a day when I finally quit. I smoked when I wasn’t sleeping or eating. I would never put a cigarette down. Always held it in my hand.
I was in the hospital two months with TB and I lit my first cigarette when walking down the steps on my way out. Then I just quit cold turkey two years after that.
Two things.
1 - To sorta address the OP - I used to smoke in the neighborhood of a pack to a pack and a half a day. However, friends used to frequently comment on how fast I would go through a smoke. While admittedly not on the level of three packs a day as mentioned in the OP - I never really thought about the time that my smoking 30 or so cigarettes a day consumed. Sad to say, but I’d put your 5 minute per smoke estimate as the upper limit for my former habit. Still, even at a blazing 3 minutes per smoke I was spending 90 minutes of each day with a cigarette in hand. This probably puts me in the middle of the pack (ha!) but I would have to say that I found the time to do so through breaks at work and frequent trips to my back porch. No smoking while working at my desk - no smoking in the apartment - just a cigarette in my mouth/hand during most other free times.
2 - The 10th of this month marked my one year anniversary of not having smoked a cigarette. Repercussions of tooting ones own horn be damned - I’m thrilled about it.
Non-smoker here - I’m just curious if any of the multi-pack-per-day folks who don’t actually smoke so much as they have a lit cigarette in their hands - is there a concern that they may be breathing more unfiltered smoke than filtered smoke?