depends on Your cells, and charger, not on the light
most cells arent worth what is imprinted on them. I have had quite SOME, rated from 2100 up to 2700 and anything over 2200 mAh @ 800 mAh fresh from the charger was not too common ...
When rested for avout 1 week, 1/2 of the cells were at the same value than Eneloop kind Ni-Mhs, thats why I switched to them for lights @ non daily use
Maybe it will finally be common to mention current draw when testing, then one can estimate runtime.
[edit]Sorry, missed that "lithium" part.
Still: (have someone) measure current draw, then calculate [/edit]