The conversion factor is approximately 2-6 times whatever the stated interval is.
Loose example of Valve Time from the Steam August 26 update news:
"Fans will remember that Blue Shift included a "High Definition Pack," a set of visually enhanced player and weapon models. We've had to iron out some technical wrinkles with how we deliver the HD Pack, but it will be made available through Steam within the next week or so."
As of November 20, 2005, this content still hasn't been released.