Check out the API of our display library: https://github.com/ThingPulse/esp8266-oled-ssd1306. setContrast() should give you what you need.
A number of our open-source applications demonstrate how you would go about obtaining the correct wall-clock time through NTP e.g. https://github.com/ThingPulse/espaper-client/blob/master/EspaperClient/EspaperClient.ino#L93
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