If you feel you have made your decision (which I am guessing Bloom had before the city game) then what does waiting achieve? Surely that just heightens the surprise. With players and managers on holiday you need every day you can get if you are taking a change in direction
I've been thinking on Hughton's sacking and think there was a degree of calculated waiting. I am starting to think maybe Bloom didn't make it clear Hughton's job was in danger because he felt it would be an unhelpful pressure added at a time when we were struggling. There were reports that Bloom was considering firing him after the Cardiff game - the back up would all have been Hughton's men since Jones had gone, or we'd have to dip down to the younger teams' managers, and how easy would it have been to bring in Potter with a handful of games left in the season? How disruptive would that have been to our efforts to stay up. Better to stick with Hughton to the end of the season and then act. He had, after all, kept us out of the relegation places up to that point, and we saw what happened with Norwich in the same situation.
Then better to act as soon as possible - for the club it gives us more time to fill the vacancy, give the incoming manager as much time as possible to prepare (look at videos of our games to get a better feel for our players, etc), move and settle in to a new home, and get a full pre-season with the players, and also means we went for him at an end point in his previous club's season, would he have been willing to come to us if he had just met up with the boys to start a new season, having signed some players sold them on Swansea's vision etc.
It also frees Hughton up for any other job that comes up. Boro, West Brom, Derby have all changed their managers, Hughton was free and able to apply for those jobs because Bloom sacked him so soon, if he had waited and instead of firing Hughton explained his misgivings and giving Hughton a chance to put forward and argument for staying, an action plan and transfer approach etc and then decided to fire him anyway, Hughton would have missed out on those opportunities. Sure, that's all moot as it appears Hughton wasn't interested in them, but it gave him that choice.