I am not sure you can run an SLA against a 'timeframe' like that. You can create SLAs on the Change Request table, though. You'd need to set your start conditions in the SLA somehow based on the planned start date. The 'duration' on the SLA is where I could see things getting tricky. You can't script the duration, as in, a duration between planned start and end dates.

You could probably achieve what you want using a workflow with some scripting and timers. It seems it may be more of an 'after close' type of thing, as you would need to know the actual start/end times to determine if there was any sort of breach.

Tim