Hey all, still new to HA and trying to work my way around 
I have created some scenes with my lights like Normal Scene for standard nighttime light and a cinema scene which will be activated, as soon as my tv goes on at nighttime.
My “problem” is, that if a scene switches, the lights dont change or go on on the same time - there is just a tiny bit of delay in them which doesnt look that smoothe… is there an easy way to adjust this, so all lights will change smoothly when a scene changes?
You can try Parallelizing Actions, but there are many things that can contribute to lights behaving as you have described. Network traffic or interference, the processing power of your server, or the strength of the mesh if you are using Zigbee or ZWave, whether you are using light groups vs. multiple individual entities(especially in Zigbee networks)…
If you share more details about the integrations and equipment you are using someone may be able to supply a more specific answer.
Are they all the same kind of lights or are some of them connected via e.g. Zigbee and others via WiFi, etc.?
Hmm mostly Ikea Tradfri or Philips HUE Lights… maybe 1 light is a Wifi Bulb. I have connected the Ikea lights via Matter and the HUE lights with the bridge
The Hue lights react immediatly and the Ikea ones are having delays after activating a scene
Just as Didgeridrew mentioned, many factors can affect the response time of a smart device. This is especially true in your case, as your lights are made by different companies. Unfortunately, there is not much you can do other than using lights from the same manufacturer that communicate through the same protocol. However, even that does not guarantee they will work in unison as you are hoping.
My first suggestion is to try turning the lights on separately to see if the delay exists outside of using a scene. I suspect you will still notice a delay with the Ikea lights. If that is the case, and assuming you are using an automation or script to activate the scene when the TV turns on, you could modify it to control the lights individually.
Instead of using an action to activate the scene, create separate actions to turn on the lights. You will likely still encounter a delay with the Ikea lights, but you can address this by adding a wait/delay action before turning on the Hue lights. So in the automation, create an action to turn on the Ikea lights, then add a wait/delay action set to 500 ms (you could adjust this later), and then create an action to turn on the Hue lights. This approach will cause a slight delay in the Hue lights turning on, but now they should all turn on together.
You will need to adjust the wait/delay time to get it just right, but once it is properly configured, everything should work as intended.
I have the same experience as almighty59 describes, but I’d guess that, even if you can figure out some timings for delays for different technologies or brands, it won’t be consistent because - at least in my case - they vary now & then, depending on how busy the overall setup is, e.g. one of your cameras might just take & save a snapshot while your automation or scene is executing: there goes your carefully crafted 324ms delay 
Another thing I’ve done for automations - back when if-then-else setups in the automation weren’t as easy as they are now - is to call several scripts from within the action flow that simply run the turn_on or turn_off actions.
This way, at least action two and three are under way in a timely fashion, even if action one hasn’t finished yet and is holding up the chain and adding to delays.
