Wouldn't worry too much about the boxwood. I have soil freeze solid on mine (Japanese, American and Korean) all winter. Some remain frozen in pots for months. No issues, foliage may bronze a bit, but the green comes back with warmer weather. I don't know about the olive, but I suspect it's OK. Short shallow freezes like the one these got hit with are rarely more than short term issues. If thing had frozen below 25 for a few days, I'd start worrying about the olive.
We're in for a killer springtime here in the eastern U.S. with the same odd conditions you've described. It was 80 F back in early Jan. We've had above average temps the last few weeks. Today and tomorrow 70's with no freezing in sight for the next week. I've got several maples and other stuff about to bud out.
Spring is NOT here. We will get a deep freeze probably at the end of the month, or in March. This happened last year and I lost some trees and had significant dieback on others.
)
