I'd say standard any% rules should apply. Timing in real time from starting the campaing to result screen after last mission. Fastest difficulty is Very Easy due to more starting money, cheaper buildings, less services required, weaker enemies. "Construction blessing" should be enabled, as it saves time on mission with pyramids and mastabas.

There's just one issue, 100% game speed is CPU dependent (about 20s per year on my PC), so better hardware can give an advantage. However playing without 100% is much too slow, so there's no other choice.