Tell Win7 to
Shutdown every day at a certain time, say 8:00am.
Then have your BIOS automatically
Startup your PC at a certain time, say 5:00pm.
Make sure you have auto-login enabled, and throw a quick batch script that starts CGMiner in the startup folder. Bam. Done.
The thing is... I don;t want every day to be the same, as mentioned in the OP.
Well that's no problem. Rather than making 1 scheduler events to shut off the PC every day, make 5 events that shut off the PC once a week.
Event 1 - Shut down the PC every Monday at 7:00am.
Event 2 - Shut down the PC every Tuesday at 8:00am.
Etc.
The BIOS alarm wakeup only works if the PC is off. If it's already on, it will just keep going.
This lets you adjust what time you want it to shut off every morning, and will also make sure it's hashing nonstop over the weekends.