Depends really...
My normal poi, I can get about 2 minutes out of them if I do not spin them too fast, or about 30 seconds if I spin like a maniac.
My "brick" poi, as my friends like to call them (cathedral or interweave wick poi with 4 foot of wick on each) will last for about 4 to 7 minutes depending on how fast I am spinning them. I cannot make these ones go out just by spinning fast as I can with most others...that and they are rather heavy (hence the "brick poi" name) and so require a lot of effort to spin fast.
If your wicks are getting old they may not burn for as long as they should either.
------------------
fe fi foo fun