I've reviewed some Hubitat logs from earlier in the day that seem to highlight the "sleepy" delay:
Dimmer was used moments earlier (i.e. "warmed up") and level is adjusted about ~200 ms after button event:
dev:332022-05-10 06:50:28.785 am infoTV Room Dimmer: level was set to 1% (digital) [actual: 1]
dev:332022-05-10 06:50:28.588 am infoTV Room Dimmer: button 4 pushed [down 2x]
After being idle for about 10 minutes level is adjusted about ~800 ms after button event:
dev:332022-05-10 06:59:39.257 am infoTV Room Dimmer: level was set to 100% (digital) [actual: 65]
dev:332022-05-10 06:59:38.449 am infoTV Room Dimmer: button 3 pushed [up 2x]
After being idle for another 30 minutes level is again adjusted about ~800 ms after button event:
dev:332022-05-10 07:27:05.020 am infoTV Room Dimmer: level was set to 1% (digital) [actual: 1]
dev:332022-05-10 07:27:04.239 am infoTV Room Dimmer: button 4 pushed [down 2x]
About 30 seconds later (i.e. "warmed up") level is again adjusted about ~200 ms after button event:
dev:332022-05-10 07:27:32.984 am infoTV Room Dimmer: level was set to 100% (digital) [actual: 65]
dev:332022-05-10 07:27:32.778 am infoTV Room Dimmer: button 3 pushed [up 2x]
These intervals are pretty consistent across longer log samples. "Cold" times are around 800 "warm" times around 200.
I wonder if the Hubitat is to blame here. That gap of time between "button pushed" and "level was set" could very well be hub processing time. I'm using Rule Machine to execute setLevel commands in response to button (scene) events. Maybe Hubitat is slow to process them when it has been idle for a while? I guess I need to increase logging of the rule execution to test that theory...
Edit: Hubitat may be the culprit?
Enabled logs for the Rule Machine rule and sure enough, the 800ms "sleepy" delay appears to be related to Hubitat rule execution:
dev:332022-05-10 02:23:01.384 pm infoTV Room Dimmer: switch was turned on (digital)
app:1412022-05-10 02:23:01.056 pm infoAction: Dim: TV Room Dimmer: 100
app:1412022-05-10 02:23:00.970 pm infoTriggered
app:1412022-05-10 02:23:00.951 pm infoEvent: TV Room Dimmer pushed 3
dev:332022-05-10 02:23:00.553 pm infoTV Room Dimmer: button 3 pushed [up 2x]
Almost 400 ms elapsed between "button 3 pushed" and the "event" log entry! Another 300+ ms between the "action" log entry and the status update from the dimmer "turned on"! Once the system is warmed up, those delays are back in the 10s of milliseconds and everything is more responsive.
Is this known/expected behavior? Hubitat may exhibit processing "warm up" delays when idle for a period of time? (In my case, about 10 minutes.)