What you could do is create a batch file, maybe call it sleep.bat with this command in it:
Then create a sheduled task to run this when you want the computer to go to sleep. This will put your computer to sleep only if hibernate is not enabled, so you may need to modify your power settings to disable hibernation.
To wake up again, create another batch file, maybe call it wake.bat. It doesn't matter the command you do, maybe just put "exit" as the only command, but when you create the scheduled task for it, make sure you check the box that says: "Wake the computer to run this task"
I hope that works for you!