Depends on the climb and amount of available free water... ground water will continue to run well below 0 as it is insulated from the crazy cold temps, and will not "freeze instantly" once it's exposed. I've climbed some of my most fun plastic ice in sub-zero conditions. If the climb isn't fed by any ground water ice growth essentially stops during these kinds of temps. The ice will become hard & brittle, and can start to "dry out". Think of the ice in the freezer if you don't cycle through it... no above freezing temps will pretty much halt any growth, where there isn't free flowing ground water...
Some good places to ferret out plastic ice IMO during these conditions:
Silver Cascade (climb close to the waterfalls for best ice)
East Face Slabs, Willard (look for the plastic lines, right next to brittle lines)-> https://www.youtube.com/watch?v=nzpVCWPPHoA
Not cold that day but SO plastic. Sorry no X position.
Texaco Slab (not reliable IMO, but sometimes)
Streamline (easy grade II)
All I can think of right now...