Ha, that sounds like my buddy who talked me into buying the fishing rod that catches more fisherman than fish. I made the same mistake with Catan years ago and learned real quick that more players just means more sitting around watching other people roll dice. The math is simple, six people means your turn comes up way less often, so a game that used to take an hour and a half now eats your whole night. My group runs four max and we are way happier for it. Dave probably gets a kickback or just really loves moving little wooden roads around for three hours. Sell that box to the next guy who thinks more is better.

Adding a splash of water to loosen it back up" yeah that never works, once Portland cement starts setting you can't bring it back. The water you add just sits there and kills the bond. But the real fix is what you mix with, not the mortar itself. In that kind of heat you want ice water in the bucket, not cold tap water. Dump a bag of ice in your water barrel and mix with that. It buys you a solid 20-30 minutes of working time. Also keep your block wet. Soak them down with the hose before you lay, because dry block sucks the moisture right out of the mortar. A wet block and ice water together and you can actually get a full course done before things go south.