[R-SIG-Finance] Scaling risk for irregularly spaced time series?

[Shane Conway]

I'm working with intraday FX price data (primarily hourly bars).  I
want to scale my volatility calculations up to the daily level.
Ordinarily I would us the square-root-of-time rule and multiple by the
sqrt(T).

The question is: how do people deal with this scaling factor when the
time series is irregularly spaced?  If I apply sqrt(24) for hourly
data but I only have 8 hours of data (for instance), my calculation
will be way off.

Thanks,
Shane