The hourly balance status is actually two different ones. One is the continuous calculation (this is from a data and balance of your choice) and the other is the one showing up on the summary page, that only calculates the hourly balance for that period.
The one on the summary page is the easiest to understand. It takes the time that you registered in Jiffy and subtract the expected work time from that value. The expected work-time is the work-hours set in settings, with respect for the specific changed work-hours that you can set in the history view for specific days.
The continuously calculation uses the same base data, i.e. the registered hours, minus the expected work-time per day, also with respect for the overrides that you might do in the history-view, but its adds and subtract hours from the last configured known balance. The known balance value is created in the settings, where you can set the day of the last known hours, and the hours itself.
Since we don’t know between which hours you are planning to work a specific day, we start each day by subtracting the running value with the expected work-time in the morning, and then we add up the registered time throughout the day. This means that if your expected work-time for today is 8 hours, you will see a minus of eight hours in the morning, and then it will move towards zero during the day. When you reach zero, you worked enough to stop for the day, but If you continue to work, it will start showing a positive time, meaning overtime. If you have positive time at the end of the day, that time will be forwarded to the next day. If you for example have 2 hours of overtime for today, next morning you will see -6 hours (assuming expected work-time is 8 hours) and you will reach the zero after just 6 hours of work that day, and might leave 2 hours earlier if allowed.