The length of daylight on a given calendar day was essentially the same as today, there are some long-term variations but they don't matter here. Three things to consider:

• 1718 was long before people agreed on specific time zones. /r/AskHistorians would be a good place to ask about timekeeping details.
• The length of the day depends on the latitude, so your own daylight hours only matter if you live at the same approximate latitude.
• Who says the rule was based on the time of sunset? Maybe the time from sunset to 8 pm had so many people still awake and/or on the streets that it wasn't important to mandate light carrying.