Guessing when it will struck the 28 billionth bet is not that bad but I think you need to have some kind of open window in which you will accept contestants as people will take advantage of the time it is nearing the goal. This promotion will really remove the chances of bots taking advantage of the previous promotions Bitsler have. But another downside is there might not be a winner at all as the possibility of their predictions might be way off compared to the actual time.
Yes, its also a good idea to put a deadline on when they can place their prediction like once bets reached a certain number of bets left to reach another milestone and not the way that they can place their prediction anytime they want and only 1 account can be used. But then again, current promo of Bitsler is still ok just like what posted above.
Yes that actually would be much smarter, and make the cut-off time like a few million bets away which is about a day or so away.
If it was done this way then most likely there wouldn't be so many people spamming the bets and it would be more fair to the everyday gamblers who use Bitsler instead of the ones that only show up during these promos.
However it would be alot of work, it would be easier just to limit the bet speed, and set a min bet size for the promo, if a small bet is won, then it would be forwarded to the next bet which met the requirement.