dicepro: As to smaller ponds, the only thing against it is the fact that Fencer doesn't want to allow it in the CreatePond form. The site handles this situation very well: Small Pond
I tried a few of these small ponds that Kunoichi created while looking for ponds and they weren't all that fun to play - much more random factor than strategy, takes most of the fun out of it in my opinion.

As to shorter time limits, I think the smallest unit so far is the hour, it would take some coding to add minute timeouts. More than that, the script that checks what ponds should move to the next turn runs hourly.