The delay seems to be in the zwave comms from Vera rather than scene execution in itself. I see similar delays sometimes when controlling single devices (no scene) from Vera. In contrast, the non z-wave stuff reacts almost instantly when running a scene: the Hue bulbs in the living room come on directly when the scene runs; the z-wave dimmers take 1 - 15 seconds more
since a week or so i tend to the same conclusion.
i have a WiFi LED Bulb in the bedroom (they have a widespread reputation that they just not reliable at all in matters of automation)
the lamp is turned on in orange at the morning via a scene IF my wife is on Morning Shift …
sort of Wakeup light.
this never failed to work (and i would actually excuse it if it would not do)
downstairs everything is z-wave
if i come home … the GPS tracking triggers a Virtual switch. the connected scene turns on the driveway light, tv backlight the dinner light and unlocks the door
in 4 out of 10 times the dinner and TV light remains off …
honestly, i could live with the delays, but if things not happen at all … thats really anoying.
funny is … the dinner light (which is always one of the failing ones) have about 2cm thick air-brick wall (no steel) and about 30cm air to the vera … where the driveway light is easy 50 meters away serwal walls, windows (including solid concrete walls) in between … but this one always works.
very odd thing this is.
What type of switch is this? From your description, it sounds like Vera is behind the switch. I have seen several switches where the antenna is in front of the switch’s metal face plate, shielding out signals from behind the switch. Leviton is especially bad for this.
I suspect that creating a (manual)route to get the signal to the switch from the front of the faceplate would improve its reliability. I would bet that there is already an automatic route to your 50 meters away switch.
What type of switch is this?[/quote]
they both Fibaro dual switches.
but as i said the one in question can literally “see” the vera 
all my routers and switches and things are in a small room behind the wall where the switch in question is, the boxes holding the switches are connected (the lightswitch in the small room and the switch outside have a direct connection (can see trough) and no metall at all (all panasonic plastic frames))
so technically there is only a sheet of plastic (the cover of the lightswitches) in the radio waves
i suspected the routes are a issue too … since vera automatically added neighbors are arround there.
i had removed all the neighbors already to test this behavour … with no change at all.
(or is removeing the node ids from the neighbor-field in advanced not enough ?)
but i do notice quite regulary vera does serval retries on basically all the switches (even on the one in the same room with JUST Air (about 30 cm) in between.) if multiple devices are beeing turned on or off.
as example … if i turn on all lights … and switch daynight to “Day” … i see alot of blue bars noting the retries.
if i manually trigger any of the switches in question, they work instantly, via dashboard or via homewave. also vera does have instant update that the status of the switch has changed of i use the physical switch.
just the scenes seem to have this problems…
my wildest guess at this moment is that the retry-settings are different if a scene execute a action.