If I invested in your site say 0.1 how much would I expect back in 24 hours?
No one will be able to give you an estimate. All depends on players' luck.
You should always see such investment as a long-term thing, sometimes very long term.
It not only depends on the players' luck, but also the total wagered amount on the site, the % of your investment in the bankroll and your risk setting.
Actually you can give an estimate on average,
this table shows the PRCDice bank is turned over every 2 days. With a 0.9% investors edge investors should gain 0.45% in 24 hours. Of Course the result in any given 24 hours varies wildly but that is the theoretical average since the 1st of October. I have not yet had a think about how leveraging and different kelly settings will affect this but it will.
More valuably
the table shows how much investors have really made in the last 93 days is 39.49% which is 0.42% per day.
So with more than 3 plus months of data the theoretical return for 24 hours is 0.45% and the actual return is 0.42%. I'll call that a pretty good estimate ON AVERAGE, in any one given day you can't say

lots good stats here by the way
http://bitcoin-betting-guide.com/gambling-investments/gambling-investments-comparison-table/