Does decreasing the interval of checks require recreating the rrd files?

Subject pretty much says it all.  If I want a more granular graphs, which checks done and graphed every 2 minutes instead of the default 5, what all do I have to change?

I'm also being asked that...if the hobbit interval is currently every 5 minutes, are client-reported alerts sent out instantly (as soon as they are received), or are they only processed during the update interval. For some very critical services, waiting 5 minutes to find out that it's down can be too long.

Thanks,
-Charles