Back Off !!
The biggest killer of calibration on torque wrenches with an internal spring is operators who do not back the torque wrench setting off after use.
The best practice is to always return the setting to just under the minimum setting. This allows the spring to return to its natural free length and will help to maintain the calibration of the wrench.
Torque wrenches that are left wound up on high torque settings will generally fail calibration tests compared to ones that have been backed off. This is simply because the free length of the spring on torque wrenches that are left wound up become shorter, therefore causing calibration drop.
Want accuracy for longer? Don't be lazy, don't say you don't have enough time, just back it off, it's up to you.