1. What is the frequency used by the this WiFi light switch?
This WiFi Light Switch uses the 2.4 GHz frequency band.

2. Is a neutral wire required with your WiFi Light Switch?
Yes, a neutral wire is required for use with this WiFi Light Switch.

3. Can I ask Alexa " turn on the bedroom light after 10 minutes" ?
Yes, Alexa has a built in timer function that will perform the action desired after telling it to wait an "x" amount of time.
To achieve this inquiry, you need to create "Routines" on the Alexa app, for details instruction, please contact the Alexa support.

For example
In Alexa app, when setup "Routines", the trigger is
Voice: Alexa, turn on the bedroom light after 10 minutes,

The action is
Wait(Action 1):set timer to 10 minutes
Device(Action 2):Turn on bedroom light

When you say the voice command "Alexa, turn on the bedroom light after 10 minutes", the bedroom light will be turned on after 10 minutes.