never heard of actual mileage.
pads are like tires. you never know what mileage you're gonna get...
so things wear down differently. if you brake hard, if you have a larger or lighter load, if you have different rotors, etc. so many different conditions. rule of thumb, if the light is there, just fix it asap. if you dont it will end up costing more than the initial repair.
if your unable to do it the next day, then i would feel like you can do at least another 1k miles.
brake pad replacement is not all that bad. its like a couple of hour job.
now if you were to also bleed in new fresh fluids, then that would take longer but also very satisfying.