[cj]

A quick Google search says otherwise. (Although I’ve been to horse tracks, Saratoga, and have bet on horses, and don’t recall the payouts changing, so maybe this is a bad source…)

> Horse racing uses a pari-mutuel system. There's a pool of money wagered, the track takes a cut and the rest is distributed to the winning bettors. But that system means you don't know what the final odds will be when you make your bet —because they are constantly changing until the race begins.

[KK7NIL]

Your quote backs up what OP said. In pari-mutuel betting the odds are decided all at once after betting has closed, hence your timing doesn't change the odds you get.

This is in contrast with fixed odds betting against the bookie where they'd adjust the odds as bets came in to hedge their position. That is no longer common.