Never timed it but I feel that the times in Garmins specs are pretty accurate if the light spends anytime in the high mode it goes crazy fast. I have gotten in the mode of always charging it every couple of rides it uses battery even when off.
Thanks, asking because in the user manual there is no spec about smart mode, just when light is on, and it says that in stand by mode last for about a year. But i think smart and stand by are different.