I bought IPO stocks as soon as the trading started.
I bought IPO stocks immediately after the trading started.
I bought IPO stocks immediately at the start of trading.
「取引開始」は「start of trading」、「start trading」といいます。
「直後」は「immediately」です。
「As soon as 〜」ともいえます。
「株」は「stock」または「share」です。
I bought IPO stocks as soon as the trading started.
取引開始直後、IPO株を買った。
I bought IPO stocks immediately after the trading started.
取引開始直後、IPO株を買った。
I bought IPO stocks immediately at the start of trading.
取引開始直後、IPO株を買った。