Don't have 10.6 here, but under 10.5 the Energy Saver System Preference has a "Schedule..." button at the lower right where you can set a time that the computer Sleeps everyday and then you can leave the regular setting set to Never.

iMac 2.7 GHz Core i5, 12 GB RAM, OS X 10.9, Int SATA 1 TB, Ext Fire 2 TB / 1 TB / 1 TB / 500 GB / 300 GB
Former MacFixIt Forums member since 11/17/99
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