I generally run every day on the build-up to a race.... but in terms of hard effort i'd usually want minimum two clear days of easy running prior to a race.... so if the weekend race was a sunday, i'd do a thursday session, but if it was a saturday race then i'd skip the thursday session.
Exception being the inter-counties this weekend where i want to be absolutely fresh... i'll do tonight's session then it will be easy all the way to sunday.
I have been slightly more reckless in the past.... in fact i got a pb by about 15mins at Roaches, less than 24hrs after running an XC fixture... and have also ran the Marsden-Edale Trigger the day after XC.... but in this year's spirit of being more sensible, it just doesn't appeal to me to hit a target race with anything less than 100% fresh legs.