Service times and durations can vary from stop to stop. If that's the case for you, you should indicate durations for each stop in your spreadsheet, or make sure to add durations manually for each stop.
The stop duration you set for an individual stop will override the default duration (see below).
If an individual stop doesn't have a specified duration, it will automatically use the default stop duration. Out of the box, Routific's default stop duration is 10 minutes. You can change that number in your settings panel (gear icon in the top right of your dashboard).