You've got a voltmeter so you're the best one to answer the "how long" question.
Your uprated headlight's not gonna be drawing more current than the standard one plus standard driving lights, and things like the GPS, tach, voltmeter, coils etc draw very little extra current. Keep an eye on the meter and if it gets low turn off things like the vest, gloves, and extra lights. Might not be a bad idea to use an ampmeter (in your workshop) to find out how much current all the relative devices draw so you know which ones to turn off first for best effect.
