As part of the original concept for UPB, the designers came up with 4 actions that can occur with a wall switch rocker - single tap, double tap, hold, and release. By adding the double tap capability, now you can do some very flexible things. For example, you can activate a link with a single tap, but deactivate the same link using a double tap. Then, the press and hold could start a fade, and the release action could stop the fade. But, by using the Custom feature, you could make any of the four actions do almost anything it's very flexible and powerful. This double tap feature is built into the base core firmware.
The issue with the delay response time is that you have to give the switch enough time to determine if the user is going to do a double tap before you start the dimming action. In the original switches, there was a delay of 750 ms to allow the switch to make sure that the user was not going to do a double tap. This was a huge topic of debate in the user community - users either loved it or hated it. So, all of the vendors - SAI, PCS, HAI, and WMT - have implemented a user adjustable delay. Now, from Upstart, if the switch version supports it, you can select 300 ms, 450 ms, 600 ms, and 750 ms (it might be slightly different for the various vendors). I think it is SAI firmware V1.13 where they implemented it, but this did not support the lower setting. Their V1.15 does support the lower setting. PCS and HAI (I think HAI did this at the same time) implemented this capability when they introduced their Gen2 switches. This is not technically a Gen2 issue - it just happened to be introduced along with the Gen2 capability.
I have talked with many users who really complained about the 750 ms setting and they really like the 300 ms setting. While they will tell you that they would like to see it be instanteous, 300 ms is pretty fast. In fact, it can be an issue putting a device into setup mode - you have to press the rocker five times very quickly. I've had guys that could not press the rocker fast enough to get it into setup mode. What I tell people to do is do all of your desired programming with the switch at 750 ms, then come back and change it to 300 once they are satisfied.
Hope this helps.