Non lasix horses have to be on course approx. 2 hours beforehand, give or take about 15 mins at each track. Lasix horses are 4 hours beforehand.
Arriving on course at least 2 hours before your race and random post race TC02 have made TC02 infractions all but extinct in North America.... they are VERY rare. The same cannot be said in the Southern Hemisphere. Arriving 2 hours before your race is just once (vital) piece of the puzzle to nip this practice in the bud.... the other being post race TC02 testing.