Yes as zerg the lost supply is counted, so you can either go 12 hatch 11 pool 10 gas or 12-12-12 if you want to be a little bit more economically greedy at the expense of making it much harder to hold 8rax in ZvT as an example.

As you get later into the game people who play more seriously also use the in-game clock, or timing a building placement relative to how complete a different building is to determine building timing. This helps with subtleties like whether you lost your scouting worker or not (-1 supply), if the early game got really weird because you had to build more units to hold some aggression, etc.