Your system uses around 14.8v (3.5ish for each led and 1 for the driver).
So its simply mAh/mA = h
You should see 4.8/.7 = around 7hrs runtime at 700mA!
But....
Not sure how well LiIon holds its voltage so things might dim down somewhat as the battery runs out. You really should have a few more volts or 1 less led. Your LEDs might use as much as 3.7 each...bflex will underdrive them in this situation.