Bounty was offered by Santino and lifted after he finishes the job. Winston had to make a decision to excommunicado Wick because he broke the rules by killing Santino inside the Continental grounds. So until bounty offer has been active, everybody tries to win it. That's why everyone was trying to kill Wick. After it was retracted, I think assassins went their own ways, went looking for jobs etc..
After the excommunicado, that's a whole different story.
Winston gave wick one hours head start to get ready/be prepared. not the assassins the ones who did that