How can I turn off all incoming call ring sounds for a specified period of time on my iPhone?

How can I turn off all incoming call ring sounds for a specified period of time?I usually turn off the ring switch on the side of my iphone when I am in the doctors office or during an important meeting.The problem is after the office visit I frequently forget to turn the ring back on thus missing important calls .How can I turn OFF all incoming phone call ring sound for a specified time eg like an hour and then it should resume ring sound again from incoming calls.It would be extremely helpful.Thanks

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