Can I control the ringer volume based on a timer/clock?
Apple does not allow apps to "play with" that system setting. That's the technical reason why there's no app for it. It might be able using a jailbreak tweak if it has to change every day (for example: monday between 2 and 4, tuesday between 2 and 3 etc.)

However if you go to:


Settings
Do not disturb
Scheduled
Pick the time of your desire
You're done