Is that the same Empire? The version I've seen has no BTUs. Just basics: random continents, cities produce military units, units require different numbers of turns for production, etc.

However, I saw a modern-ish decendent called Empire Deluxe, so maybe the original had more features?

The version I played all those years ago definitely had BTUs. I remember planning ahead of time what the most efficient use of them would be, before actually doing things between updates; not to mention setting alarms to wake me up, log on, and use up the (otherwise wasted because I was at max) ones at times in the night, if I was doing something, er… sneaky :)

TIL :)