After some more thought, I had to change my answer...
For the first question, you would set up an In-Queue Call Flow (copy the default, or create a new one) which plays Hold Music for 10 seconds (a setting on the Hold Music action), then uses a Transfer to Flow action to transfer the call to your main IVR flow. That should accomplish what you want.
The second question is a little trickier...IVR doesn't know anything about the phone receiving the call. Architect just hands the call off to the rest of the system (ACD queue processing, or transfer to a user or station processing, whatever you program in). So, there is no concept of "Send it to a WebRTC phone" or "Send it to a cell phone"...it just sends to a queue or a user or a station, and whatever type of phone is in use is what it goes to.
That said, you can customize a Task in Architect with logic to look at the time of day and decide what Action to use. Use a Decision or Switch action to test the current date time and decide which path to take from there. Use Transfer to ACD, Transfer to User, Transfer to Number, or whatever else may be appropriate from there.