Warned my crew about troweling mortar that's been sitting too long, learned it the hard way on a chimney job in Dayton
Left a half batch of type N sitting in the tub for about 50 minutes while we cut some brick, and it set up faster than I expected once it hit the wall. Started adding a splash of water to bring it back and the bond was garbage by the second course. Now I dump anything past 30 minutes, no matter how small the batch.