Congratulations! You are asking the wrong question about every sentence.
1. It's a mess.
2. No. '...18 hours straight.' word order
3. Depends on context. Perfect tenses relate past events to other events that happen later. The later event(s) are not mentioned.
4. "Place"? Perhaps you mistyped 'plane'- an easy mistake but one you should catch yourself. Would turbulence cause the flight attendant to spill coffee earlier or later (or at any different time)? No, so "at that time" is redundant.
4a. Would she have spilled more coffee if there had been no turbulence? Probably not, so 'the flight attendant spilled coffee on my shirt'...
Student or Learner