The low voltage warning of the Shrediquette starts LED blinking when the voltage drops below a parameter you can set in TriGUI. Don't use the low voltage warning as a timer. You should consider it as an emergency alert. Some LiPos have a very steep voltage drop after a very plain curve so you might only have 5 to 10 seconds from warning to crash depending on the LiPo.
Instead try measuring the average fly time and use the countdown of your sender, a mobile phone countdown or a stopwatch to time your flight time. Try flying for 5 min and recharge the LiPo and calculate the power consumtion per minute. Now calculate how mucht time you can fly until you have 20% of power left in the LiPo.
This might sound very difficult but it is the only way to get along with the different voltage curves of the LiPos. Additionally your LiPo will have a longer lifetime because they don't like to be copletely discharged.