As a rule of thumb, you should only be selling back to the grid when you are generating PV in excess of your loads and need to charge batteries. When your TOU period is in effect, you should be generating any PV (depending on time of the year) to run your loads and charge or discharge the battery, but not be selling from the battery. And if you have a period of time say at night where your rate is very low, then you can set this period to charge batteries up to say 70-80% SOC in case there is a cloudy day and you may not generate enough PV to avoid high TOU rates.