As a native (American) English speaker, "half two" is nonsense to me, but if I had to guess at a time the closest thing would be "half past two" (2:30), so I'd

As a native (American) English speaker, "half two" is nonsense to me, but if I had to guess at a time the closest thing would be "half past two" (2:30), so I'd probably guess that first. I'd never heard anyone say "half until two" or "half to two" and they're both incredibly awkward. "quarter after", "half past", and "quarter til" are the ones we use.