Time needed to present a poster
In general, depends on the conference's poster presentation format. Check the guidelines for a given timespan. If there is none, then it is probably no presentation, but a normal poster session where you are presenting your poster in parallel with a lot of other people in a room. People will come by and you can explain your work to them.

In such a scenario, I would not assume to do a fully linear presentation. Rather I'd prepare a very short topic introduction (at most a minute, better 30 seconds). Then check back with your visitor if they seem interested or are asking questions already. 
Then based on interaction with your visitor, try to find out which aspects of your work are interesting to them and drill deeper in the respective direction. 

Poster sessions are very much about direct interaction, so don't try to shower everyone with a whole bucket of water as soon as they arrive, give them small sips and see if they like your wine. If they do, you may end up empyting whole bottles with one or two of them and drunkenly end up in a bar in the evening to plan your collaboration. Most people will just nod and smile to your short intro and be happy to go on.

P.S. If you can present all your content in about 5 minutes that's however a good indication that you've chosen about the right level of abstraction - I'd just cut it in smaller pieces that you can dish out individually/as layers.