In law, ex post facto is used to refer to something done after the fact. I'm interested to know what Latin phrase would mean done during or simultaneously with the fact.
Perhaps surprisingly, ex post factō isn't actually a valid Latin phrase on its own: it's got two prepositions in a row, and Latin doesn't allow that.
So why do people use it? Well, in legal Latin, a law made after the fact is a postfactum, a "thing-made-after". So a punishment originating from one of these laws comes ex postfactō, "from a thing-made-after".
If you want to adapt this phrase, you could use the adverb simul, "at the same time". Something made at the same time as another thing could, perhaps, be a *simulfactum, or a simultāneum; I like the second option more because it's attested in mediaeval Latin and rolls off the tongue a bit better. And a punishment originating from one of these could, perhaps, come ex simultāneō.