I'm making the assumption that you're testing the pex for use in a concrete slab? If not, you can ignore the rest of my note.
If so, I left mine pressurized with the gage visible for the concrete guy to see while he poured the slab (I was not present for the pour).
If you're having someone else pour your concrete, point out the gage and the current pressure. Make sure he realizes it's holding pressure now and that you expect it to still be holding pressure when he is finished.
Both contractors who did my two shops wanted me to leave the system pressurized. They kept an eye on it during the pour. They said if a pressure drop was noticed, they knew there was a problem and they'd locate and isolate the leak.
You shouldn't have anything to worry about as pex is pretty tough stuff and you really have to try hard to damage it. Keeping it pressurized during the pour is just a good precaution and provides peace of mind. If a careless contractor happens to cut a tube when it's not pressurized, you won't know until it's too late.