The best time to charge your iPhone is quite flexible, as modern iPhones with Lithium-ion batteries can be charged whenever you want without waiting for the battery to drain completely or reach full charge. Here are key points to consider for optimal charging and battery health:

• You can safely charge your iPhone at any battery level; for example, charging when it's at 40% and unplugging at 80% won't harm the battery.
• Apple recommends keeping the battery charge between 20% and 80% to minimize battery wear and extend lifespan.
• It’s not necessary to wait until 100% to unplug the device and you don’t need to fully drain it to 0% regularly.
• Charging overnight is perfectly fine because iPhones have built-in mechanisms to stop charging when reaching 100%, preventing overcharge.
• iOS has an "Optimized Battery Charging" feature that slows charging after 80% when charging overnight and resumes closer to the time you typically use the device, which helps prolong battery life.
• Avoid leaving your iPhone unused for long periods without charging; if storing for a while, keep it around 50% charged.
• Use high-quality chargers and cables (preferably Apple-certified) for safety and optimal charging.

In summary, you should charge your iPhone as often as you like based on convenience, ideally before it drops below 20%, and unplug when convenient without worrying about reaching 100% every time. Charging overnight with Optimized Battery Charging enabled is also a good practice.