5-10 minutes difference with sincere intention is NOT an issue when considering that the dawn thread appears at different times to people based on point of elevation.
The fast is not dependent on the mechanical clock.
And mechanical clock times are NOT actual times - when considering the fact that the time on the clock setting is dependent on bundled longitudinal time zones.
During Ramadan, daytime fasting for Muslims ends at sunset. But for Dubai’s Burj Khalifa, the tallest building in the world, the Sun sets four minutes later at the top than at the bottom.
High-floor dwellers see beyond the ground-level horizon, farther along Earth’s curvature.
In theory time zones are based on the division of the world into twenty four time zones of 15 degrees longitude each.
The time convention begins with Universal Coordinated Time (UTC) which is also commonly referred to as Greenwich Mean Time (GMT) being located at the Greenwich meridian.
The time in each successive time zone is one hour different from the times in neighboring time zones.
To establish time zones, Earth's rotation rate of 360 degrees of longitude per day was divided by 24 hours. The result shows that Earth turns 15 degrees of longitude per hour.