How much are you dosing? When I was manually dosing I would dose them on the same day at different times, usually about 1/2 hour apart from each other. It's best to dose each supplement at different times so the one can thoroughly mix in your system before adding the other to prevent any abiotic precipitation.
I wouldn't dose them at the same time in the same place, but you don't have to separate them by a day. When I was doing it manually, I would pour one part in my sump and the other in my overflow a few seconds later. No problems with precipitation.