My iPhone 4 used to always have these kinds of delays when I was trying to exit a processor-intensive app. I don't know if it's a bug, or an issue, but it has definitely been around for a while.Yea that is when I noticed it most
This actually helped me. I had triple click VoiceOver in xDWell. It will always have some delay.
It needs to wait for two clicks to invoke multitask bar. Back when there is no multitask, click home button once and it will go home instantly. You can try setting triple click in accessibility to see how long it will take to go home. This time it will have to wait for three clicks so it will have a long delay. Hope this help.