30 people send 0.1 each at the same time... all in the same block.
Oh and upper limits don't make sense at all, since one can easily just bet from different addresses.
Even the value of the Dow Jones is not very random and it also doesn't change every second of the day. Also I'm not too sure if you can even get quotes down to the second there.
At the time when 30 are thirty people purchasing tickets (actually, well before then) I will introduce no limit daily (or hourly) lotteries. This means the limit won't matter anymore.
And yes, I understand the upper limit doesn't make any sense in that you can bypass it. I was actually thinking of removing it since you can easily get around it.