Odd since 2 Ice shards should take 2.80 seconds and 3 Frost Breaths is 2.43 seconds. Also not how damage is calculate:
https://pokemongo.gamepress.gg/damage-mechanics
" Between two equally matched Pokemon, "½ Power + 1" is a good estimate of actual damage"
So everything else being equal 2 Ice shards would be 9+9, 3 Frost Breaths would be 6+6+6 so same damage more time to dodge