There's a big variety of firms related to Wall Street and making money. Since OP mentioned "timing the market", I assume OP meant the high-frequency trading (HFT) mentioned in books like "Flash Boys" and "Dark Pools."
Generally when someone "times the market", it means they react to news event and think they're first to take advantage. But they're not - some HFT firm already took advantage before the story made national news. And other HFT firms are also too late - some studies show the profit off an event goes to the first trade.
HFT firms aren't limited to a zero sum game. If a buyer and seller are trying to find each other in the market, HFT firms are often standing between the two. They give some liquidity, but often it's for meaningless amounts of time. They profit off pushing prices slightly away from what the two parties would agree on together. A second approach may or may not still be available: rewarding transaction volume. HFT firms maneuver in ways that seem wrong, but have been allowed, and they take much of the rewards an exchange offers.
There's a lot of nuance to HFT that isn't covered by calling it a zero sum game, or saying it's just timing the market. I'd encourage reading the popular book "Flash Boys" or more in depth and interesting "Dark Pools" to see some of the subtler things HFT does that hurt other market participants. But also some context: it's much better to have HFT firms providing millisecond liquidity and eating up fractions of a cent than the very old approach of rounding every share price off to 1/8th or 1/16th of a dollar.