this came up at my institution this week too... the Cubicin monograph in the CPS has this:
Chemical and physical in-use stability on the reconstituted solution in the vial, or infusion solutions, has been demonstrated for 12 hours at 25°C and up to 10 days if stored under refrigeration (2 to 8°C), under normal lighting conditions. However, because CUBICIN does not contain any preservative or bacteriostatic agent, aseptic technique must be used during preparation for administration and the product should be used promptly. If the reconstituted product is not used immediately, it must be refrigerated at 2 to 8°C. It is recommended that the solution be used within 72 hours due to the possibility of microbial contamination during reconstitution. Avoid excessive heat.
The combined time (vial and infusion bag) at room temperature, up to 25°C, should not exceed 12 hours. The combined time (vial and infusion bag) at 2-8°C should not exceed 10 days.
So we keep extra reconstituted vials/bags in the fridge for up to 10 days. NB: this is a Canadian reference, maybe our arctic conditions lend themselves to better antibiotic stability? Har har...