Then look clearly how far she's gotten from the car's initial position. The anime showed 30 seconds. With this it is enough for her to get back to the car. start the engine, and go for about 3 meters, pretending she just passed by.
If you think clearly enough, there are more than one reason for what ever time limit she put in that bomb.
1. Gin's suspicion - This would make her time the bomb not to long so that he wouldn't suspect her.
2. Akai's escape (If and only if Gosho intended for Akai to live) - Making the time long enough for an escape.
3. Timing the police car to notice the explosion - If too long the police would have passed Akai's car, but, they can still turn around to check. If they didn't notice the dead body (If the car's door was closed, then there would be less visibility for the police, and Gin's camera of course). But If the timing was too early, the effect would be the same, except she would have been suspicious and there is a possibility that the police will chase her. (If I were the police, I will first contact HQ or an ambulance/fire truck to the scene and then chase the suspect. But that's not the case now isn't it?)
The thing here is that the timing was exact. Now, setting aside of what was the intention of the exact timing (It is still possible that it was accidental). Gin saw the police first before Kir placed the bomb. That means from the the time it took where Gin saw the police to Akai's car, It would be the same as the time in the bomb.
If it took the police 10 seconds to get there, that means Kir had to get to her car to that position pass the police car by a bit within 10 seconds. Then the 3 seconds showing Akai to Gin you keep saying that was needed in order to clear of suspicion would have been unnecessary, or probably couldn't have been accomplished in time, I can't tell since i still don't know how long it would take her to get to that point.
If it was 30 seconds, then she either waited for something, or was just slow. The reason, I don't know. They didn't show it. Or It wasn't really 30 seconds. Perhaps less, perhaps more.
Then how long do you think would a switch of bodies be needed? It still depends on the trick, If there ever was one, that was done.
Where, exactly is Gin's camera? What were the blind spots he had, from whether something blocked something(clothes), or when she tilted her body in order to shoot, or when she looked at the police cars.
I still don't have a conclusion but I'm pretty sure it's not impossible for Akai to have lived.
Remember to eliminate the impossible...(you should know what comes next

)