There is a delay for smaller bets. 99 satoshi and lower get 0.1s delay, 9 and lower have 0.5s delay, and 0 satoshi bets have 2s delay.
Other than that, bet speed only depends how fast you can communicate with the servers, which in turn depends where you connect from and on your connection quality.
May I ask what is the purpose of zero satoshi bets?
About the progressive jackpot - I think it would be cool if you have multiple progressive jackpots versions designed and allow players to choose what variant they want to use.
It would be absolutely amazing feature to have, that level of customization would be truly next level!