Neuropolarbear has a post up suggesting that people presenting posters at scientific meetings should know how to give the short version of their poster.
My favorite time to see posters is 11:55 and 4:55, since then people are forced to keep it short.
If you are writing your poster talk right now, remember to use a stopwatch and make your 5 minute version 5 minutes.
Don't even practice a longer version.
I have a suggestion.
Ask the person to tell you why they are there! Really, this is a several second exchange that can save a lot of time. For noobs, sure, maybe this is slightly embarrassing because it underlines that even if you have managed to scope out the name successfully you do not remember that this is some luminary in your subfield. Whatever. Suck it up and ask. It saves tremendous time.
If you are presenting rodent behavioral data and the person indicates that they know their way around an intravenous self-administration procedure, skip the methods! or just highlight where you've deviated critically from the expected paradigms. If they are some molecular douche who just stopped by because "THC" caught their eye then you may need to go into some detail about what sort of paradigms you are presenting.
Similarly if it is someone from the lab that just published a paper close to your findings, just jump straight to the data-chase. "This part of figure 2 totally explains what you just published"
Trust me, they will thank you.
As Neuropolarbear observes, if you've skipped something key, then this person will ask. Poster sessions are great that way.