Suggestion Re Call extensions
Well this is possible
All you need to do is to opt for manual bidding instead of automatic bidding (because that way you don't have option to schedule your ads) under the campaign settings for which you are enabling Call Extensions.
After that go to campaign settings>>Advanced Settings>>Ad Scheduling. Click on edit here and choose the time period, days when you want to show your ads. Click on save and that's it. You can read more about this here. Doing this will ensure that your ads are running for working hours when you want and hence call extensions will also appear during the sametime.
NOTE: In order to run your campaign all time, you can create a separate campaign for non working hours without call extensions.
I hope you have set up the call extensions from the Ad Extensions tab.
Just a thought!
This is a feature request that has come up a few times in the past. It makes complete sense to bring it in as well.
The only current way around it (I think) is to have 2 campaigns, one with call extensions and one without and use the scheduling to switch the campaigns at a certain time of the day.