as was said...
;)
I like to expand my arena with small bits at a time. It could be coincidential but I think that the longer the expansion is expected to take, the more chance you have it takes a (much) longer time. Usually I keep my expansions at 6 or 7 days estimate.
The way I think it works is like this: every day a calculation is made to see if the expansion progressed a day or not. Chances are high this is true, but you also have a chance it is false. If it is false the daycount stays the same. If the dayscount hits 0, the expansion is complete.
the more days the calculation needs to be done, the more chance you have to come out false a few times, and the longer it takes.
In the end if you make 5 expansions of 6 days, and you result in 6days, 7 days, 8 days, 8 days and 7 days for completion (which is a realistic example for BB), you always have your expansion within 2 days of the estimate. If you do an expansion of 30 days, with the same luck, you will have it ready by day 36, which means 6 days late! Even though it is the same result, if feels a lot longer.
Further, in the rules it says that bigger expansions will take longer, which might result in more chance for the formula to come out false if they programmed it that way...
They are not your friends; they dispise you. I am the only one you can count on. Trust me.