Scott,
As long as the lights go off when the c02 does

I agree that the c02 run time PRIOR to lights on is also vital. My c02 goes on about 90 minutes before lights on.
I would agree with Jonny that about 60-90 minutes would be the max I would be comfortable turning off the c02 while leaving the lights on esp at the same rate/intensity.
If you reduce the intensity for this time when c02 is off, it is another story, but I still think it is not a good idea. I think that c02 does not stay in solution long, so the amount in the tank will quickly be used, and then a deficiency exists.
We have learned the importance of c02 and how changing levels affect the amount of Rubisco produced by the plants. Why take the chance that these may be affected for no apparent purpose?
I would not recommend leaving your lights on for 4 hrs with n0 c02.