Depends on person
Everyone's sensitivity to caffeine
That being said, why would you ingest a lot of caffeine if your were trying to fall asleep? Best way to fall asleep as it relates to caffeine: don't consume caffeine less than 5-6 hours before planned bedtime (the 1/2 life of caffeine is about 5-6 hours). Some people can't consume caffeine after lunchtime to make sure it's out of system by bed.