A person pours a cup of hot coffee intending to drink it five minutes later to keep it as hot as possible should he put cream in it now or wait until just before he drinks it?

Wait. The coffee is already being exposed to many cooling factors before you drink it. The cup you are pouring it into cools it initially, followed by the air temperature while in transit. The best thing to do is seal the coffee in in insulated cup, mug or thermos and add cream only when you're ready to enjoy it.